Journal articles: 'Magnetic Interaction - Transition Metal Complexes'

1

Heit, Yonaton N., Dumitru-Claudiu Sergentu, and Jochen Autschbach. "Magnetic circular dichroism spectra of transition metal complexes calculated from restricted active space wavefunctions." Physical Chemistry Chemical Physics 21, no. 10 (2019): 5586–97. http://dx.doi.org/10.1039/c8cp07849a.

Full text

Abstract:

Multiconfigurational restricted active space (RAS) self-consistent field (SCF) or configuration interaction (CI) approaches, augmented with a treatment of spin–orbit coupling by state interaction, were used to calculate the magnetic circular dichroism , , and/or for closed- and open-shell transition metal complexes.

APA, Harvard, Vancouver, ISO, and other styles

2

Echeverría, Jorge. "The n → π* interaction in metal complexes." Chemical Communications 54, no. 24 (2018): 3061–64. http://dx.doi.org/10.1039/c8cc00763b.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Pelletier, Yanick, and Christian Reber. "Single-crystal absorption spectroscopy of binuclear complexes of iron(III) and manganese(III) with the μ-oxo-bis(μ-acetato)dimetal core." Canadian Journal of Chemistry 73, no. 2 (February 1, 1995): 249–54. http://dx.doi.org/10.1139/v95-034.

Full text

Abstract:

Single-crystal absorption spectroscopy at variable temperature is used to determine exchange couplings between transition metal centers in both the electronic ground and excited states in two new homobimetallic complexes with the formula [LM(μ-O)(μ-CH3CO2)2ML′](ClO4)2, where M is iron(III) or manganese(III). L and L' denote 1,4,7-triazacyclononane and 1,4,7-trimethyl-1,4,7-triazacyclononane, respectively. Values for the ground state exchange coupling constant J are −295 cm−1 and +10 cm−1 for the iron and manganese compounds, respectively, using Hex = −JS1•S2. Exchange interactions in excited states are qualitatively analyzed, indicating that a spin-forbidden transition of the Fe–Fe binuclear unit occurs with significant intensity by the single-ion mechanism, and not as expected by the Tanabe pair intensity mechanism for spin-forbidden transitions, the dominant mechanism for isoelectronic complexes of manganese(II). Keywords: absorption spectra, exchange interaction, magnetic properties, bimetallic complexes of iron(III), bimetallic complexes of manganese(III)

APA, Harvard, Vancouver, ISO, and other styles

4

Pierpont, Cortlandt G., and Attia S. Attia. "Spin Coupling Interactions in Transition Metal Complexes Containing Radical o-Semiquinone Ligands. A Review." Collection of Czechoslovak Chemical Communications 66, no. 1 (2001): 33–51. http://dx.doi.org/10.1135/cccc20010033.

Full text

Abstract:

Transition metal complexes ofo-semiquinone (SQ) ligands have been studied extensively over the past 25 years. A particularly interesting aspect of this coordination chemistry concerns magnetic interactions between paramagnetic metal ions and the radical anionic ligands. In this review we begin with a survey of relatively simple complexes consisting of a paramagnetic metal ion chelated by a single SQ ligand. Recent studies have revealed the importance of SQ-SQ coupling through diamagnetic metals, and complexes of this class are described in the second section of the review. Both interactions combine to account for the often complicated magnetic properties of complexes containing multiple SQ ligands chelated to a paramagnetic metal ion. Research on these complexes is surveyed in the third section with a concluding look toward polymeric SQ complexes. A review with 51 references.

APA, Harvard, Vancouver, ISO, and other styles

5

Weheabby, Saddam, Mohammad A. Abdulmalic, Matteo Atzori, Roberta Sessoli, Azar Aliabadi, and Tobias Rüffer. "Promotion of antiferromagnetic exchange interaction in multinuclear copper(ii) complexes via fused oxamato/oxamidato ligands." Dalton Transactions 47, no. 45 (2018): 16164–81. http://dx.doi.org/10.1039/c8dt03691h.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Flores, Sonia, and D. E. Ellis. "Magnetic Interactions in Dimeric Transition Metal Complexes: Basicerythro-Chromium(III)." Inorganic Chemistry 37, no. 24 (November 1998): 6346–53. http://dx.doi.org/10.1021/ic981049x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Boča, Roman, Ivan Nemec, Ivan Šalitroš, Ján Pavlik, Radovan Herchel, and Franz Renz. "Interplay between spin crossover and exchange interaction in iron(III) complexes." Pure and Applied Chemistry 81, no. 8 (July 20, 2009): 1357–83. http://dx.doi.org/10.1351/pac-con-08-07-20.

Full text

Abstract:

In the dinuclear and polynuclear metal complexes exhibiting the low-spin (LS) to high-spin (HS) transition, the spin-crossover phenomenon interferes with the magnetic exchange interaction. The latter manifests itself in forming spin-multiplets, which causes a possible overlap of the band originating in different reference spin states (LL, LH, HL, and HH). A series of dinuclear Fe(III) complexes has been prepared; the iron centers are linked by a bidentate bridge (CN-, and diamagnetic metallacyanates {Fe(CN)5(NO)}, {Ni(CN)4}, {Pt(CN)4}, and {Ag(CN)2}). Magnetic measurements confirm that the spin crossover proceeds on the thermal propagation. This information has been completed also by the Mössbauer spectral (MS) data. A theoretical model has been developed that allows a simultaneous fitting of all available experimental data (magnetic susceptibility, magnetization, HS mole fraction) on a common set of parameters.

APA, Harvard, Vancouver, ISO, and other styles

8

El-Ghamry, Hoda A., Mohamed Gaber, and Thoraya A. Farghaly. "Synthesis, Structural Characterization, Molecular Modeling and DNA Binding Ability of CoII, NiII, CuII, ZnII, PdII and CdII Complexes of Benzocycloheptenone Thiosemicarbazone Ligand." Mini-Reviews in Medicinal Chemistry 19, no. 13 (August 21, 2019): 1068–79. http://dx.doi.org/10.2174/1389557519666190301143322.

Full text

Abstract:

Background & Objective: Six novel complexes of transition metal namely, [CoLCl2(H2O)2]0.5H2O, [NiLCl2(H2O)2]0.5H2O, [CuLCl2]0.5H2O, [ZnLCl2], [PdLCl2]H2O and [CdLCl2]H2O, where L is benzocycloheptenone thiosemicarbazone ligand, have been obtained. The confirmation of the structures of the obtained metal chelates depends on the different spectral and physicochemical techniques including CHN analysis, infrared spectra, molar conductivity measurement, UV-vis, thermogravimetric analysis and magnetic moment. The infrared spectral results ascertained that the ligand behaved as neutral bidentate connecting the metal centers via N and S atoms of C=N and C=S groups, respectively. Methods: The UV-Vis, molar conductivity and magnetic susceptibility results implied that the geometrical structures of the metal chelates are octahedral for Co(II) & Ni(II) complexes, tetrahedral for Zn(II) & Cd(II) complexes and square planar for Cu(II) & Pd(II) complexes which have been confirmed by molecular modeling studies. Conclusion: Moreover, the mode of interaction between some chosen metal complexes towards SSDNA has been thoughtful by UV-Vis spectra and viscosity measurements. The value of the intrinsic binding constant (Kb) for the examined compounds has been found to be lower than the binding affinity of the classical intercalator ethedium bromide. Also, the viscosity measurements of the complexes proved that they bind to DNA, most likely, by a non-intercalative mode like H-bonding or electrostatic interactions.

APA, Harvard, Vancouver, ISO, and other styles

9

Ananyev, Ivan V., Nadezhda A. Bokach, and Vadim Yu Kukushkin. "Structure-directing sulfur...metal noncovalent semicoordination bonding." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 76, no. 3 (May 21, 2020): 436–49. http://dx.doi.org/10.1107/s2052520620005685.

Full text

Abstract:

The abundance and geometric features of nonbonding contacts between metal centers and `soft' sulfur atoms bound to a non-metal substituent R were analyzed by processing data from the Cambridge Structural Database. The angular arrangement of M, S and R atoms with ∠(R—S...M) down to 150° was a common feature of the late transition metal complexes exhibiting shortened R—S...M contacts. Several model nickel(II), palladium(II), platinum(II) and gold(I) complexes were chosen for a theoretical analysis of R—S...M interactions using the DFT method applied to (equilibrium) isolated systems. A combination of the real-space approaches, such as Quantum Theory of Atoms in Molecules (QTAIM), noncovalent interaction index (NCI), electron localization function (ELF) and Interacting Quantum Atoms (IQA), and orbital (Natural Bond Orbitals, NBO) methods was used to provide insights into the nature and energetics of R—S...M interactions with respect to the metal atom identity and its coordination environment. The explored features of the R—S...M interactions support the trends observed by inspecting the CSD statistics, and indicate a predominant contribution of semicoordination bonds between nucleophilic sites of the sulfur atom and electrophilic sites of the metal. A contribution of chalcogen bonding (that is formally opposite to semicoordination) was also recognized, although it was significantly smaller in magnitude. The analysis of R—S...M interaction strengths was performed and the structure-directing role of the intramolecular R—S...M interactions in stabilizing certain conformations of metal complexes was revealed.

APA, Harvard, Vancouver, ISO, and other styles

10

Chalmers, James E., Anant Kumar Srivastava, Richard J. C. Dixey, Krrishna Sivakumaran, and Paul J. Saines. "Low dimensional and frustrated antiferromagnetic interactions in transition metal chloride complexes with simple amine ligands." CrystEngComm 21, no. 5 (2019): 894–901. http://dx.doi.org/10.1039/c8ce01901k.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Malenov, Dušan P., Jelena P. Blagojević Filipović, and Snežana D. Zarić. "Stacking interactions of the methylated cyclopentadienyl ligands in the crystal structures of transition metal complexes." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 76, no. 2 (March 19, 2020): 252–58. http://dx.doi.org/10.1107/s2052520620002206.

Full text

Abstract:

In the crystal structures of methylated cyclopentadienyl (Cp) complexes (MeCp, Me4Cp and Me5Cp) deposited in the Cambridge Structural Database, certain orientation types of stacked contacts can be noted as the most frequent. These orientation preferences can be well explained by the matching of oppositely charged regions of electrostatic potential. Parallel displaced stacking, large offset stacking and C—H...π interactions are the dominant interaction types that are responsible for the arrangement in the crystal structures of stacked methylated Cp complexes.

APA, Harvard, Vancouver, ISO, and other styles

12

Basavaraju, Bennehalli, and Halehatti S. Bhojya Naik. "Synthesis and Thermal Degradation Kinetics of Co(II), Ni(II), Cd(II), Zn(II), Pd(II), Rh(III) and Ru(III) Complexes with Methylquinolino[3,2-b]benzodiazepine." E-Journal of Chemistry 4, no. 2 (2007): 199–207. http://dx.doi.org/10.1155/2007/808902.

Full text

Abstract:

A series of new complexes formed by the interaction of a new ligand Methylquinolino[3,2-b]benzodiazepine (L) with various transition metal ions have been isolated and characterized by elemental analysis and electronic, IR, magnetic moment and conductivity measurements. Thermogravimetric (TG) studies of the complexes have been performed in order to establish the mode of their thermal degradation. The thermal degradation was found to proceed in two steps. The kinetics and thermodynamic parameters were computed from the thermal decomposition data.

APA, Harvard, Vancouver, ISO, and other styles

13

Bencini, Alessandro, Federico Totti, Claude A. Daul, Karel Doclo, Piercarlo Fantucci, and Vincenzo Barone. "Density Functional Calculations of Magnetic Exchange Interactions in Polynuclear Transition Metal Complexes." Inorganic Chemistry 36, no. 22 (October 1997): 5022–30. http://dx.doi.org/10.1021/ic961448x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Gao, Yue, Yu-Qin Li, Yao Li, Jing-Wei Dai, Jin-Hua Wang, Ying-Ying Wu, Masahiro Yamashita, and Zhao-Yang Li. "Diverse Magnetic Properties of Two New Binuclear Complexes Affected by [FeN6] Octahedral Distortion: Two-Step Spin Crossover versus Antiferromagnetic Interactions." Magnetochemistry 9, no. 3 (February 28, 2023): 69. http://dx.doi.org/10.3390/magnetochemistry9030069.

Full text

Abstract:

Polymetallic complexes with covalently bridged metal centers that interact magnetically are important in the molecular magnetism field, with binuclear compounds receiving special attention because they represent the simplest type of multinuclear species with covalently bridged metal centers. Herein, we report the synthesis and properties of two new binuclear FeII complexes, namely, {[Fe(abpt-TPE)(NCS)2]2(bpym)}·2MeOH·2MeCN (1) and {[Fe(abpt-TPE)(NCS)2]2(bpym)}·2CH2Cl2 (2) (bpym = 2,2′-bipyrimidine). The crystal structure is analyzed at different temperatures, and its properties are analyzed by variable-temperature magnetic susceptibility and variable-temperature fluorescence emission spectroscopy tests. Variable-temperature magnetic susceptibility measurements of two binuclear compounds show different types of magnetic behavior. Complex 1 exhibits two-step spin transition behavior with an intermediate state near 150 K (Tc1 = 191 K, Tc2 = 111 K); 1 undergoes an [LS–LS] ↔ [LS–HS] ↔ [HS–HS] spin transition during thermal induction. On the other hand, complex 2 exhibits intramolecular antiferromagnetic coupling, with J = −0.47 cm−1. The analysis of correlations between the structural characteristics and different types of magnetic behaviors for two binuclear complexes, revealed that the different magnetic behaviors shown by the two complexes are attributable to different degrees of [FeN6] octahedral distortion caused by different lattice solvents, ligand strain and crystal stacking.

APA, Harvard, Vancouver, ISO, and other styles

15

Sunjuk, Mahmoud, Lana Al-Najjar, Majed Shtaiwi, Bassam El-Eswed, Mousa Al-Noaimi, Luay Al-Essa, and Kamal Sweidan. "Transition Metal Complexes of Schiff Base Ligands Prepared from Reaction of Aminobenzothiazole with Benzaldehydes." Inorganics 10, no. 4 (March 30, 2022): 43. http://dx.doi.org/10.3390/inorganics10040043.

Full text

Abstract:

Schiff bases have played significant roles in the development of inorganic or coordination chemistry. Three Schiff base (NB, CB and HB) ligands, prepared for the reaction of 2-amino-6-methoxy-benzothiazole with 2-Nitrobenzaldehyde, 2-chlorobenzaldehyde and 2,4-Dihydroxybenzaldehyed, respectively, were investigated for their transition metal complexes, which were prepared by reacting the ligand (2:1 molar ratio) with Co(II), Ni(II), Cu(II), Cd(II), Cr(III) and Fe(III) chlorides. The nature of the interaction between the metal ions and ligands (L) was studied with the aid of magnetic susceptibility, elemental analysis, FTIR and 1H-NMR spectroscopy. Based on the magnetic superstability and elemental analysis results, octahedral structures of the complexes, such as [ML2Cl2] or [ML2Cl(OH)], were proposed for Cu(II), Cd(II), Co(II) and Ni(II) in which the ligand (L:NB, CB or HB) is bidentate through the azomethine and benzothiazole nitrogen. For Cr(III) and Fe(III) complexes, octahedral ML2Cl(OH)2 or ML2(OH)3 structures were proposed, where one ligand is monodentate and the other is bidentate. The azomethine ν(-HC=N-) and 1H-NMR peaks of NB and CB were shifted to a higher frequency and downfield, respectively, upon complexation with metal ions. The bonding of OH groups of HB to Co(II), Cu(II) and Ni(II) enables π-backdonation from these metals to the azomethine of Schiff bases and the consequent shift of ν(-HC=N-) to a lower frequency and changes in the intensity of the 1H-NMR peak of OH. On the other hand, this backdonation was not evidenced in the FTIR of HB complexes with high-charge Cr(III) and Fe(III) ions.

APA, Harvard, Vancouver, ISO, and other styles

16

Klokishner, Sophia, Serghei Ostrovsky, Andrew Palii, and Boris Tsukerblat. "Cooperative Spin Transitions Triggered by Phonons in Metal Complexes Coupled to Molecular Vibrations." Magnetochemistry 8, no. 2 (February 8, 2022): 24. http://dx.doi.org/10.3390/magnetochemistry8020024.

Full text

Abstract:

The present article is a short overview of the theoretical modeling of spin transitions in polymetallic compounds. As distinguished from many insightful reviews on this topic, the present work is focused on the nature of cooperative interaction of the metal clusters in molecular crystals with emphasis at the physical role of molecular vibrations and phonons. The underlying model assumes that the cooperativity is triggered by phonons while the metal centers are coupled to molecular vibrations. It is demonstrated that the suggested model gives a satisfactory description of the observed spin transitions in mono-, bi- and tetranuclear compounds. In the framework of the described approach, we discuss the experimental data on spin crossover in the mononuclear [Fe(ptz)6](BF4)2, binuclear [{Fe(bt)(NCS)2}2bpym] and tetranuclear [Fe(tpa){N(CN)2}]4·(BF4)4·(H2O)2 compounds containing iron ions. The approach is also applied to the description of the charge-transfer-induced spin transition in the [{(Tp)Fe(CN)3}{Co-(PY5Me2)}](CF3SO3) complex.

APA, Harvard, Vancouver, ISO, and other styles

17

Yahsi, Yasemin. "X-ray characterization and magnetic properties of dioxygen-bridged CuIIand MnIIISchiff base complexes." Acta Crystallographica Section C Structural Chemistry 72, no. 7 (June 24, 2016): 585–92. http://dx.doi.org/10.1107/s2053229616008974.

Full text

Abstract:

The coordination chemistry of multinuclear metal compounds is important because of their relevance to the multi-metal active sites of various metalloproteins and metalloenzymes. Multinuclear CuIIand MnIIIcompounds are of interest due to their various properties in the fields of coordination chemistry, inorganic biochemistry, catalysis, and optical and magnetic materials. Oxygen-bridged binuclear MnIIIcomplexes generally exhibit antiferromagnetic interactions and a few examples of ferromagnetic interactions have also been reported. Binuclear CuIIcomplexes are important due to the fact that they provide examples of the simplest case of magnetic interaction involving only two unpaired electrons. Two novel dioxygen-bridged copper(II) and manganese(III) Schiff base complexes, namely bis(μ-4-bromo-2-{[(3-oxidopropyl)imino]methyl}phenolato)dicopper(II), [Cu2(C10H10BrNO2)2], (1), and bis(diaqua{4,4′-dichloro-2,2′-[(1,1-dimethylethane-1,2-diyl)bis(nitrilomethanylylidene)]diphenolato}manganese(III)) bis{μ-4,4′-dichloro-2,2′-[(1,1-dimethylethane-1,2-diyl)bis(nitrilomethanylylidene)]diphenolato}bis[aquamanganese(III)] tetrakis(perchlorate) ethanol disolvate, [Mn(C18H16Cl2N2O2)(H2O)2]2[Mn2(C18H16Cl2N2O2)2(H2O)2](ClO4)4·2C2H5OH, (2), have been synthesized and single-crystal X-ray diffraction has been used to analyze their crystal structures. The structure analyses of (1) and (2) show that each CuIIatom is four-coordinated, with long weak Cu...O interactions of 2.8631 (13) Å linking the dinuclear halves of the centrosymmetric tetranucelar molecules, while each MnIIIatom is six-coordinated. The shortest intra- and intermolecular nonbonding Mn...Mn separations are 3.3277 (16) and 5.1763 (19) Å for (2), while the Cu...Cu separations are 3.0237 (3) and 3.4846 (3) Å for (1). The magnetic susceptibilities of (1) and (2) in the solid state were measured in the temperature range 2–300 K and reveal the presence of antiferromagnetic spin-exchange interactions between the transition metal ions.

APA, Harvard, Vancouver, ISO, and other styles

18

Aliabadi, Azar, Bernd Büchner, Vladislav Kataev, and Tobias Rüffer. "The interplay between spin densities and magnetic superexchange interactions: case studies of mono- and trinuclear bis(oxamato)-type complexes." Beilstein Journal of Nanotechnology 8 (October 27, 2017): 2245–56. http://dx.doi.org/10.3762/bjnano.8.224.

Full text

Abstract:

For future molecular spintronic applications the possibility to modify and tailor the magnetic properties of transition-metal complexes is very promising. One of such possibilities is given by the countless derivatization offered by carbon chemistry. They allow for altering chemical structures and, in doing so, to tune magnetic properties of molecular spin-carrying compounds. With emphasis on the interplay of the spin density distribution of mononuclear and magnetic superexchange couplings of trinuclear bis(oxamato)-type complexes we review on efforts on such magneto-structural correlations.

APA, Harvard, Vancouver, ISO, and other styles

19

Minaev, Boris F., and Hans Ågren. "Spin-Orbit Coupling Induced Chemical Reactivity and Spin-Catalysis Phenomena." Collection of Czechoslovak Chemical Communications 60, no. 3 (1995): 339–71. http://dx.doi.org/10.1135/cccc19950339.

Full text

Abstract:

The crucial role of electron spin in the control of the reaction channels in the region of activated complexes can easily be inferred from the general principles of chemical bonding. Magnetic perturbations could change spin at the intermediate stages of a reaction or in the region of activation barriers and could hence influence the reaction rate through spin switching of the reaction paths. Spin-orbit coupling is one of the most important intrinsic magnetic perturbations in molecules; its role in chemical reactivity is here shown by a few typical examples. Spin-orbit coupling induced spin flip could also be important in catalysis by transition metals. General qualitative arguments predict great enhancements of the spin-orbit coupling in catalytic complexes with transition metal compounds. The concept of spin-catalysis is introduced in order to describe and classify a wide range of phenomena in which chemical reactions are promoted by substances assisting in inducing spin changes and overcoming spin-prohibition. This concept is based on results of quantum chemical calculations with account of spin-orbit coupling and configuration interaction in the intermediate complexes. Besides spin-orbit coupling, the role of intermolecular exchange interaction with open shell catalysts is stressed. The catalytic action would definitely depend on the efficiency of spin uncoupling inside the reacting substrate molecule and this could be induced by magnetic and exchange perturbations.

APA, Harvard, Vancouver, ISO, and other styles

20

Timken, Mark D., William A. Marritt, David N. Hendrickson, Robert A. Gagne, and Ekk Sinn. "Magnetic exchange interactions in binuclear transition-metal complexes of a binucleating clathrochelate ligand." Inorganic Chemistry 24, no. 24 (November 1985): 4202–8. http://dx.doi.org/10.1021/ic00218a044.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Ishida, Takayuki, Shin-Ichi Mitsubori, Takashi Nogami, and Hiizu Iwamura. "Intramolecular Magnetic Interaction of Transition Metal ions in Complexes Containing Pyrimidine or Pyrazine as a Bridging Ligand." Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals 233, no. 1 (September 1993): 345–50. http://dx.doi.org/10.1080/10587259308054976.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Feng, Yijun, Jincheng Zhang, Yongbing Pei, Qiu Chen, Yue Yan, and Lianbin Wu. "A Novel Strategy to Tune Magnetic Properties of Nickel(II)-Schiff Base Coordination Bridged Polysilsesquioxane." Science of Advanced Materials 11, no. 12 (December 1, 2019): 1705–11. http://dx.doi.org/10.1166/sam.2019.3600.

Full text

Abstract:

In this paper, liquid state solvent-free organosilica-based nickel-bithiazole complexes (PBSIBTHM-Ni2+, PBSIBTMeM-Ni2+) were synthesized through sol–gel processes respectively, and these two metal complexes and their precursors were characterized. The precursors with bithiazole were successfully prepared, their inorganic and organic parts were connected on molecular level. The DSC results indicated they would all exist in liquid phase at temperature ranging from 180 K to 280 K. The UV-VIS showed that a red shift of the main electronic transitions from 254 to 268 nm of PBSIBTHM to PBSIBTHM-Ni2+, Δν = 14 (from 249 to 266 nm of PBSIBTMeM to PBSIBTMeM-Ni2+, Δν = 17). This verified the formation of a more extensive π→π* conjugating system due to coordination interaction between Ni2+ and PBSIBTHM or PBSIBTMeM. The magnetic measurement results of PBSIBTHM-Ni2+ and PBSIBTMeM-Ni2+ reflected they both exhibited ferromagnetic properties at low temperature. For PBSIBTMeM-Ni2+, it had a transition temperature (Ttran) at 160 K, and became an anti-ferromagnet above Ttran. For PBSIBTHM-Ni2+, it had a very high Curie-Weiss temperature (Tc = 253 K). This strategy was expected to find potential application in fabricating the complexes with desired physicochemical properties.

APA, Harvard, Vancouver, ISO, and other styles

23

Uba, Bala, C. Muhammad, A. Uba, and A. A. Muhammad. "SYNTHESIS, GRAVIMETRIC ANALYSIS AND ANTIMICROBIAL STUDIES OF TRANSITION METALS (Cu(II), Zn(II)) COMPLEXES OF SCHIFF DERIVED FROM 2-HYDROXY-1-NAPHTHALDEHYDE AND 2-AMINO-3-METHYLPYRIDINE." FUDMA JOURNAL OF SCIENCES 5, no. 4 (January 28, 2022): 251–59. http://dx.doi.org/10.33003/fjs-2021-0504-812.

Full text

Abstract:

The interaction between 2-hydroxy-1-naphthaldehyde with 2-amino-3-methylpyridine give an orange- yellow Schiff base and its metals complexes of Cu (II) and Zn (II) were green and dark-green respectively, both Schiff base and metals complexes were characterized using different analytical techniques such as melting point, solubility test, conductivity, measurement, magnetic susceptibility measurement, IR spectroscopy and TGA. The Schiff base and its respective metal complexes showed a sharp melting point and are soluble in ethanol, dimethylsulfuroxide and methanol but insoluble in water and slightly soluble in other solvent. The conductivity value obtained revealed that the synthesized complexes are non-electrolytes while an octahedral geometry was suggested for all complexes based on the data obtained from magnetic susceptibility analysis. The IR results revealed bands at 1596 cm-1 indicating the formation of azomethine (C=N) confirming the formation of Schiff base. 747 cm-1, 773 cm-1, for (M-N) while 465 cm-1, 469 cm-1 for (M-O) bands in the spectra of the complexes supporting coordination of Schiff base to respective metals. The thermo-gram (TGA) data of all complexes, exhibited three stages of decomposition which include loss of water, decomposition of the complexes and the formation of metal (II) oxide as the final product/residue. The in vitro antimicrobial screening of Schiff base and its metals complexes showed that they are potent antimicrobial agents against the tested microorganisms

APA, Harvard, Vancouver, ISO, and other styles

24

Sharfalddin, Abeer A., Inas M. Al-Younis, Abdul-Hamid Emwas, and Mariusz Jaremko. "Investigating the Biological Potency of Nitazoxanide-Based Cu(II), Ni(II) and Zn(II) Complexes Synthesis, Characterization and Anti-COVID-19, Antioxidant, Antibacterial and Anticancer Activities." Molecules 28, no. 16 (August 18, 2023): 6126. http://dx.doi.org/10.3390/molecules28166126.

Full text

Abstract:

In this work, the biological potency of nitazoxanide (NTZ) was enhanced through coordination with transition metal ions Cu(II), Ni(II), and Zn(II). Initially, complexes with a ligand-metal stoichiometry of 2:1 were successfully synthesized and characterized by spectroscopic techniques and thermogravimetric methods. Measurement of the infrared spectrum revealed the bidentate nature of the ligand and excluded the possibility of the metal ion—amide group interaction. Nuclear magnetic resonance spectra showed a reduction in the NH- intensity signal and integration, indicating the possibility of enolization and the formation of keto-enol tautomers. To interpret these results, density functional theory was utilized under B3LYP/6-311G** for the free ligand and B3LYP/LANL2DZ for the metal complexes. We used UV-Vis and fluorescence spectroscopy to understand the biological properties of the complexes. This showed stronger interactions of NTZ-Cu(II) and NTZ-Ni(II) with DNA molecules than the NTZ-Zn(II) compound, with a binding constant (Kb) for the copper complex of 7.00 × 105 M−1. Both Cu(II)- and Ni(II)-NTZ had functional binding to the SARS-CoV-2 (6LU7) protease. Moreover, all metal complexes showed better antioxidation properties than the free ligand, with NTZ-Ni(II) having the best IC50 value of 53.45 μg/mL. NTZ-Ni(II) was an effective antibacterial, with a mean inhibitory concentration of 6 μM, which is close to that of ampicillin (a reference drug). The metal complexes had moderated anticancer potencies, with NTZ-Cu(II) having IC50 values of 24.5 and 21.5 against human breast cancer cells (MCF-7) and cancerous cervical tumor cells (HeLa), respectively. All obtained complexes exhibited high selectivity. Finally, the metal ions showed a practical role in improving the biological effectiveness of NTZ molecules.

APA, Harvard, Vancouver, ISO, and other styles

25

Baligar, Rajesh, and Vidyanand Revankar. "Coordination diversity of new mononucleating hydrazone in 3d metal complexes: synthesis, characterization and structural studies." Journal of the Serbian Chemical Society 71, no. 12 (2006): 1301–10. http://dx.doi.org/10.2298/jsc0612301b.

Full text

Abstract:

The mononucleating hydrazone ligand LH3, a condensation product of salicyloylhydrazine and (2-formylphenoxy)acetic acid, was synthesized and its coordination behavior with first row transition metal(II) ions was investigated by isolating and elucidating the structure of the complexes using elemental analysis, conductivity and magnetic susceptibility measurements, as well as IR, 1H-NMR, electronic and EPR spectral techniques. The ligand forms mononuclear metal(II) complexes of the type [CoLH(H 2O)2], [NiLH(H 2O)2], [CuLH] and [ZnLH]. The ligand field parameters, Dq, B and ? values, in the case of the cobalt and nickel complexes support not only the octahedral geometry around the metal ion, but also imply the covalent nature of the bonding in the complexes. The EPR study revealed the presence of a spin exchange interaction in the solid copper complex and the covalent nature of the bonding. The 1H-NMR study of the zinc(II) complex indicated the non-involvement of the COOH group in the coordination. The physico-chemical study supports for the presence of octahedral geometry around cobalt(II), nickel(II) and tetrahedral geometry around copper(II) and zinc(II) ions. .

APA, Harvard, Vancouver, ISO, and other styles

26

Keil, Philip M., and Terrance J. Hadlington. "Accessing cationic tetrylene-nickel(0) systems featuring donor–acceptor E–Ni triple bonds (E = Ge, Sn)." Chemical Communications 58, no. 18 (2022): 3011–14. http://dx.doi.org/10.1039/d2cc00422d.

Full text

APA, Harvard, Vancouver, ISO, and other styles

27

Krisyuk, Vladislav V., Samara Urkasym Kyzy, Tatyana V. Rybalova, Ilya V. Korolkov, Mariya A. Grebenkina, and Alexander N. Lavrov. "Structure and Properties of Heterometallics Based on Lanthanides and Transition Metals with Methoxy-β-Diketonates." Molecules 27, no. 23 (December 1, 2022): 8400. http://dx.doi.org/10.3390/molecules27238400.

Full text

Abstract:

The possibility of obtaining volatile polynuclear heterometallic complexes containing lanthanides and transition metals bound by methoxy-β-diketonates was studied. New compounds were prepared by cocrystallization of monometallic complexes from organic solvents. Ln(tmhd)3 were used as initial monometallic complexes (Ln = La, Pr, Sm, Gd, Tb, Dy, Lu; tmhd = 2,2,6,6-tetramethylheptane-3,5-dionate) in combination with TML2 in various ratios (TM = Cu, Co, Ni, Mn; L: L1 = 1,1,1-trifluoro-5,5-dimethoxypentane-2,4-dionate, L2 = 1,1,1-trifluoro-5,5-dimethoxy-hexane-2,4-dionate, L3 = 1,1,1-trifluoro-5-methoxy-5-methylhexane-2,4-dionate). Heterometallic complexes of the composition [(LnL2tmhd)2TM(tmhd)2] were isolated for light lanthanides Ln= La, Pr, Sm, Gd, and L= L1 or L2. By single crystal XRD, it has been established that heterometallic compounds containing La, Pr, Cu, Co, and Ni are isostructural linear coordination polymers of alternating mononuclear transition metal complexes and binuclear heteroleptic lanthanide complexes, connected by donor–acceptor interactions between oxygen atoms of the methoxy groups and transition metal atoms. A comparison of powder XRD patterns has shown that all heterometallic complexes obtained are isostructural. Havier lanthanides Ln = Tb, Dy, Lu did not form heterometallics. Instead, homometallic complexes Ln(L3)3 were identified for Ln = Dy, Lu as well as for Ln = La. The thermal properties of the complexes were investigated by TG-DTA and vacuum sublimation tests. The heterometallic complexes were found to be not volatile and decomposed under heating to produce inorganic composites of TM oxides and Ln fluorides. In contrast, Ln(L3)3 is volatile and may be sublimed in a vacuum. Results of magnetic measurements are discussed for several heterometallic and homometallic complexes.

APA, Harvard, Vancouver, ISO, and other styles

28

Serebryanskaya, Tatiyana V., Hanna A. Belavusava, Yuri V. Grigoriev, Sergei V. Voitekhovich, Ludmila S. Ivashkevich, and Oleg A. Ivashkevich. "Synthesis, structure and characterisation of late transition metal complexes with 2-(tetrazol-1-yl)pyridine." Journal of the Belarusian State University. Chemistry, no. 2 (September 13, 2022): 38–51. http://dx.doi.org/10.33581/2520-257x-2022-2-38-51.

Full text

Abstract:

Complexes [MII(2-pytz)Cl2] (M(II) = Pt, Pd; 2-pytz = 2-(tetrazol-1-yl)pyridine) were synthesised via direct interaction of the corresponding metal chlorides (K2PtCl4 or PdCl2) with 2-pytz under ambient conditions. RuCl3 does not react with 2-pytz under reflux in the protic media, while under reflux in N, N-dimethylformamide in the presence of LiCl, decomposition of the tetrazole cycle occurred leading to the formation of Ru(III)-coordinated N, N-dimethyl-N ′-(pyridin-2-yl)formimidamide derivative Li[RuIII(Py — N =C — NMe2)2Cl2]. The complex [Ru(2-pytz)(DMSO)3Cl2] ⋅ MeOH, where DMSO is dimethyl sulfoxide, was synthesised by reacting a specially prepared precursor cis-[Ru(DMSO)4Cl2] with 2-pytz in methanol under reflux conditions. The complex [Ru(2-pytz)(DMSO)2Cl2] was synthesised by reacting cis-[Ru(DMSO)4Cl2] with 2-pytz in ethanol under reflux conditions. The resulting complexes were characterised by elemental analyses, electrospray ionisation mass-spectrometry with detection of positive and negative ions, infrared spectroscopy, 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, and simultaneous thermal analysis. The structures of complexes [Pd(2-pytz)Cl2] and [Ru(2-pytz)(DMSO)3Cl2] ⋅ MeOH were investigated by single-crystal X-ray analysis. In the former, 2-pytz shows a N,N-chelating coordination via the pyridine ring N and the tetrazole ring N2 atoms. In the latter, 2-pytz coordinates as a monodentate ligand via the tetrazole ring N4 atom. According to 1H NMR spectroscopy data, in complex [Ru(2-pytz)(DMSO)2Cl2], 2-pytz coordinates as a N, N-chelating ligand via the pyridine ring N and the tetrazole ring N2 atoms.

APA, Harvard, Vancouver, ISO, and other styles

29

Saito, Toru, Manami Fujiwara, and Yu Takano. "Quantitative Assessment of rPM6 for Fluorine- and Chlorine-Containing Metal Complexes: Comparison with Experimental, First-Principles, and Other Semiempirical Results." Molecules 23, no. 12 (December 15, 2018): 3332. http://dx.doi.org/10.3390/molecules23123332.

Full text

Abstract:

We report a reparameterization of PM6 parameters for fluorine and chlorine using our training set containing transition metal complexes. Spin unrestricted calculations with the resulting rPM6 (UrPM6) were examined quantitatively using two test sets: (i) the description of magnetic interactions in 25 dinuclear metal complexes and (ii) the prediction of barrier heights and reaction energies for epoxidation and fluorination reactions catalyzed by high-valent manganese-oxo species. The conventional UPM6 and UPM7 methods were also evaluated for comparison on the basis of either experimental or computational (the UB3LYP/SVP level) outcomes. The merits of UrPM6 are highlighted by both the test sets. As regards magnetic exchange coupling constants, the UrPM6 method had the smallest mean absolute errors from the experimental data (19 cm−1), followed by UPM7 (119 cm−1) and UPM6 (373 cm−1). For the epoxidation and fluorination reactions, all of the transition state searches were successful using UrPM6, while the success rates obtained by UPM6 and UPM7 were only 50%. The UrPM6-optimized stationary points also agreed well with the reference UB3LYP-optimized geometries. The accuracy for estimating reaction energies was also greatly remedied.

APA, Harvard, Vancouver, ISO, and other styles

30

Moneo-Corcuera, Andrea, Breogán Pato-Doldan, Irene Sánchez-Molina, David Nieto-Castro, and José Ramón Galán-Mascarós. "Crystal Structure and Magnetic Properties of Trinuclear Transition Metal Complexes (MnII, CoII, NiII and CuII) with Bridging Sulfonate-Functionalized 1,2,4-Triazole Derivatives." Molecules 26, no. 19 (October 4, 2021): 6020. http://dx.doi.org/10.3390/molecules26196020.

Full text

Abstract:

Here we present the synthesis, structure and magnetic properties of complexes of general formula (Mn)(Me2NH2)4][Mn3(μ-L)6(H2O)6] and (Me2NH2)6[M3(μ-L)6(H2O)6] (M = CoII, NiII and CuII); L−2 = 4-(1,2,4-triazol-4-yl) ethanedisulfonate). The trinuclear polyanions were isolated as dimethylammonium salts, and their crystal structures determined by single crystal and powder X-ray diffraction data. The polyanionic part of these salts have the same molecular structure, which consists of a linear array of metal(II) ions linked by triple N1-N2-triazole bridges. In turn, the composition and crystal packing of the MnII salt differs from the rest of the complexes (with six dimethyl ammonia as countercations) in containing one Mn+2 and four dimethyl ammonia as countercations. Magnetic data indicate dominant intramolecular antiferromagnetic interactions stabilizing a paramagnetic ground state. Susceptibility data have been successfully modeled with a simple isotropic Hamiltonian for a centrosymmetric linear trimer, H = −2J (S1S2 + S2S3) with super-exchange parameters J = −0.4 K for MnII, −7.5 K for NiII and −45 K for CuII complex. The magnetic properties of these complexes and their easy processing opens unique possibilities for their incorporation as magnetic molecular probes into such hybrid materials as magnetic/conducting multifunctional materials or as dopant for organic conducting polymers.

APA, Harvard, Vancouver, ISO, and other styles

31

Ambrosius, Frank, Elke Klaus, Torsten Schaller, and Angelika Sebald. "CP/MAS NMR of Heavy Spin-1/2 Nuclei at B0 = 2.35T." Zeitschrift für Naturforschung A 50, no. 4-5 (May 1, 1995): 423–28. http://dx.doi.org/10.1515/zna-1995-4-515.

Full text

Abstract:

Perspectives of CP/MAS NMR at low external magnetic field (B0=2.35T) are discussed. Applications are illustrated for the case of heavy spin-1/2 nuclei such as 195Pt and 199Hg: 195Pt and 199Hg CP/MAS spectra of a variety of organometallic compounds are reported. Aspects of shielding anisotropics, of 195Pt-35/37Cl interactions and of 31P-M (M=Cd, Hg, Pt) coupling in transition metal phosphine complexes will be briefly addressed

APA, Harvard, Vancouver, ISO, and other styles

32

H. Sumrra, S., M. Anees, A. Asif, M. N. Zafar, K. Mahmood, M. F. Nazar, M. Khalid, M. A. Nadeem, and M. U. Khan. "Synthesis, structural, spectral and biological evaluation of metals endowed 1,2,4-triazole." Bulletin of the Chemical Society of Ethiopia 34, no. 2 (October 28, 2020): 335–51. http://dx.doi.org/10.4314/bcse.v34i2.11.

Full text

Abstract:

Biologically active triazole Schiff base ligand 2,4-dichloro-6-[(1H-1,2,4-triazol-3-ylimino)methyl]phenol (A) has been synthesized by the condensation reaction of an equimolar amount of 1H-1,2,4-triazole-3-amine and 3,5-dichlorosalicylaldehyde and then it coordinated with salts of metals [VO(IV), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II)] in 2:1 molar ratio to derive a series of transition metal chelates (1)-(6). All the compounds were characterized by various physical, spectral, analytical techniques and elemental analysis. Spectral characterization and magnetic moment data of complexes revealed square pyramidal geometry for vanadium complex and octahedral for remaining (2)-(6) complexes. Quantum chemical calculation has been carried out to explore optimized geometry and electronic structure of the ligand. Density functional theory (DFT) with B3LYP/6-311+g(d,p) method was performed to determine vibrational bands, frontier molecular orbitals (FMOs) and natural bond analysis (NBO) of the ligand. NBO analysis showed that the ligand bears higher molecular stability because of hyper conjugate interactions. Computational study results revealed that there was a close interaction of theoretical and experimental spectroscopic data. Global reactivity descriptors calculated by the energies of FMOs, indicated ligand to be bioactive. The synthesized compounds were studied for antibacterial, antifungal, antioxidant and antiglycation activity and the results revealed that ligand has remarkable activity which considerably increased upon chelation. KEY WORDS: Triazole ligand, Transition metal chelates, Antibacterial, Antifungal, Antioxidant, Computational study Bull. Chem. Soc. Ethiop. 2020, 34(2), 335-351 DOI: https://dx.doi.org/10.4314/bcse.v34i2.11

APA, Harvard, Vancouver, ISO, and other styles

33

Tchougréeff, A. L., and A. V. Soudackov. "Effective Hamiltonian crystal fields: Present status and applicability to magnetic interactions in polynuclear transition metal complexes." Russian Journal of Physical Chemistry A 88, no. 11 (October 10, 2014): 1904–13. http://dx.doi.org/10.1134/s0036024414110053.

Full text

APA, Harvard, Vancouver, ISO, and other styles

34

WEI, HAIYAN, and ZHIDA CHEN. "MAGNETIC EXCHANGE IN POLYNUCLEAR TRANSITION METAL SYSTEM: AB INITIO CASPT2 AND DENSITY FUNCTIONAL THEORY STUDY ON TRIANGULAR COPPER(II) COMPLEXES." Journal of Theoretical and Computational Chemistry 05, spec01 (January 2006): 501–14. http://dx.doi.org/10.1142/s0219633606002428.

Full text

Abstract:

The magnetic exchange interactions for five representative triangular Copper(II) complexes: antiferromagnetic Cu 3( TiPB )6 (1), [ Cu 3(μ3- OH )( aaat )3( H 2 O )3]2+ (2), [ PPN ]2 [ Cu 3(μ3- O )(μ- pz )3 Cl 3] (3), [ PPN ][ Cu 3(μ3- OH )(μ- pz )3 Cl 3] (4) and ferromagnetic [ Cu 3(2- CH 3 C 6 H 4 CO 2)4{( C 2 H 5)2 NC 2 H 4 O }2 H 2 O ] (5) are investigated by using density functional theory combined with broken-symmetry approach (DFT-BS) and ab initio CASPT2 method. Our calculated results show that DFT-BS has remarkable dependence on the particular chosen XC functionals and is system-dependent, while the calculations at CASPT2 level of theory are able to give the accurate magnetic coupling constants. Qualitatively, the two theoretical methods reproduce consistently the linear correlation between the magnetic coupling constants and the departure of the (μ3- O ) oxygen atom from the { Cu3 } plane in the complexes (3) and (4). Spin population analyses reveal that the DFT-BS method overestimates the spin electronic delocalization from the Cu(II) center to the bridging ligands.

APA, Harvard, Vancouver, ISO, and other styles

35

Maurice, Rémi, Coen de Graaf, and Nathalie Guihéry. "Theoretical determination of spin Hamiltonians with isotropic and anisotropic magnetic interactions in transition metal and lanthanide complexes." Physical Chemistry Chemical Physics 15, no. 43 (2013): 18784. http://dx.doi.org/10.1039/c3cp52521j.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

Xu, Hai Yun, Chun Hua Hu, Qi Feng Liu, Wen Xian Zhao, and Ying Liu. "Synthesis, Properties of Gadolinium Double-Decker Sandwich-Type Complex Containing Tetrabenzoporphyrin Ligand." Applied Mechanics and Materials 190-191 (July 2012): 571–74. http://dx.doi.org/10.4028/www.scientific.net/amm.190-191.571.

Full text

Abstract:

A novel gadolinium double-decker sandwich-type complex with tetrabenzoporphyrin (TBP) ligands-Gd(TBP)2 was synthesized by the reaction of porphyrin 1 with Gd(acac)3. nH2O in boiling 1, 2, 4-Tcb for 15~17 h under Ar. Its structure is characterized byUv-Vis-NIR and HR-MS. The spectroscopic properties show that the longest-wavelength visible band (600-800 nm) and the strong near-IR absorption band centered near 1340 nm of Gd (TBP)2 complex are obviously red-shifted due to the extension of the π conjugated systems derived from the linear benzoannulation in the TBP ring. The magnetic studies also indicate that the observed value of χMT of Gd(TBP)2 complex is close to the combined value of Gd(III) and porphyrin radical anion at room temperature, and antiferromagnetic interaction that possibly results from the intramolecular spin exchange between the porphyrin π-radical electron, and the gadolinium f unpaired electrons dominates its magnetic properties over the whole temperature range. Since the first report of bis(porphyrinato) metal complexes M(Por)2 such as a cerium(IV) bisporphyrinate, Ce(TPP)2 and hydrogen praseodymium(III), PrH(TPP)2 in 1983[1], sandwich-type rare earth complexes with porphyrin ligands have received increasing attentions due to the unusual physical, spectroscopic, redox, electron transfer, and/or conductivity properties resulting from their strong π-π interactions[2-4]. Whereas the chemistry and properties of homoleptic sandwich complexes containing the same pophyrinato ligands of various lanthanide, actinides and group 4 transition metals have been extensively studied[5-6], actually all of them are confined to the sandwich-type complexes containing meso-substituted porphyrin ligands except for octaethylporphyrin (OEP) or octamethylporphyrin (OMP). Little is known about sandwich-like complexes with aromatic ring-fused porphyrin ligands that contain a more delocalized π system. In this paper, we will describe the preparation of a novel gadolinium homoleptic double-decker sandwich-type complex with tetrabenzoporphyrin (TBP) ligand (see Fig.1) as well as their spectroscopic characterization and magnetic studies.

APA, Harvard, Vancouver, ISO, and other styles

37

Mathur, Neha, Nisha Jain, and A. K. Sharma. "Synthesis, Characterization and Biological Analysis of Some Novel Complexes of Phenyl Thiourea Derivatives with Copper." Open Chemistry Journal 5, no. 1 (December 31, 2018): 182–95. http://dx.doi.org/10.2174/1874842201805010182.

Full text

Abstract:

Introduction: Copper is a very important metal because all forms of life require copper metals an essential micronutrient. Various biological processes, directly or indirectly are dependent on copper metal. Methods: Copper soaps are used as fungicides, bacteriosides, herbicides and insecticides. Copper complexes including heterocyclic compounds have attracted our attention in a magnificent way because of its utility in catalysis and biological functions. Their mechanism of synthesis, characterization and structural insight, are crucial for comprehending the criteria of the bonding and electronic interactions between the proximate metal center and chelating atoms. But still, there is a need to explore some of more biological properties for their wide applicability and significant usage in multiple fields because it is an untapped area with potentially tremendous value. Hence, in this paper, we report the synthesis and characterization of transition metal complex of N/S ligand by chromatographic, FT-IR, NMR, ESR, elemental analysis, conductometric and magnetic moment measurements. Results: The synthesized metal complexes namely copper palmitate with 4-nitrophenylthiourea and copper palmitate with 4-methoxyphenylthiourea were successfully investigated for biological activities against fungi Candida albicans and Trichoderma harzinum. Based on the results, we pronounced biocidal activities of the novel complexes. Conclusion: It is concluded that the activity of nitro phenylthiourea complex has greater antifungal activity than methoxy phenylthiourea complex against these test fungi. We can conclude that the antifungal activity of these complexes varies according to the nature of the groups attached to the ligands.

APA, Harvard, Vancouver, ISO, and other styles

38

Rao, Chebrolu P., Sharada P. Kaiwar, and M. S. Srinivasa Raghavan. "Transition metal saccharide chemistry: synthesis, spectroscopy, electrochemistry and magnetic studies of chromium(III)-hexose complexes and their in vitro interaction with DNA." Polyhedron 13, no. 12 (June 1994): 1895–906. http://dx.doi.org/10.1016/0277-5387(94)80013-8.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Kharwar, Ruby, and Ritu B. Dixit. "Transition Metal Complexes of N-(4-(N-(8-Hydroxyquinolin-5-yl)sulfamoyl)phenyl)acetamide ligand: Synthesis, Characterization, in silico, in vitro Antimicrobial and DNA Binding Studies." Asian Journal of Organic & Medicinal Chemistry 5, no. 1 (2020): 20–29. http://dx.doi.org/10.14233/ajomc.2020.ajomc-p238.

Full text

Abstract:

A new, N-(4-(N-(8-hydroxyquinolin-5-yl)sulfamoyl)phenyl)acetamide (8HQSPA) ligand and its metal chelates with transition metal salts of Cu(II), Ni(II), Zn(II), Co(II), Fe(II) and Mn(II) was synthesized. The synthesized 8HQSPA ligand was characterized by mass, FT-IR, 1H NMR, 13C NMR and its metal chelates by studying their physico-chemical properties, elemental analysis, FT-IR, thermogravimetric (TG) analysis, UV-visible absorption spectroscopy and magnetic susceptibility. Thermogravimetric analysis result evident presence of two water molecules in the coordination which gives the idea of octahedral geometry and also electronic spectra showed transitions in ligand field and charge transfer bands. in silico ADMET studies was carried out to know the biological potential of synthesized compounds as it helps in development of drug candidate with fewer side effects. Molecular docking studies was carried out on bacterial proteins (PDB ID: 5h67, 3ty7, 3t88 and 5i39) and DNA helix (PDB ID: 1BNA) to predict its inhibitory effect and role on integration of DNA helix. Results showed least binding energy score (kcal/mol), which indicate that their potential of binding is greater in receptor of proteins and binds DNA through intercalation mode, which was further assessed by in vitro experiments. Antibacterial studies were carried out in the form of minimum inhibitory concentration (MIC), the results showed increased biological activity of free ligand on metal complexation in the following order: Cu > Fe > Zn > Ni > Co > Mn > 8HQSPA. Also interaction of complexes with CT-DNA was carried out by viscosity measurement, electronic absorption titration and gel electrophoresis, showed intercalation mode of binding.

APA, Harvard, Vancouver, ISO, and other styles

40

Kusz, Joachim, Maria Nowak, Robert Bronisz, and Grzegorz Szklarz. "Crystal structures of 2D coordination networks in [M(bbtr)3](ClO4)2(M=Mn, Cd)." Acta Crystallographica Section A Foundations and Advances 70, a1 (August 5, 2014): C1361. http://dx.doi.org/10.1107/s2053273314086380.

Full text

Abstract:

[Fe(bbtr)3](ClO4)2 (bbtr=1,4-di(1,2,3-triazol-1-yl)butane) represents a spin crossover (SCO) system where the first coordination sphere consists of 1,2,3-triazole rings coordinated by exodentate nitrogen atoms [1]. Iron(II) ion is linked to six other iron(II) ions by bbtr ligands. This creates two dimensional (2D) polymeric layers. SCO is abrupt, accompanied by hysteresis loop. In the cooling mode P-3 -> P-1 structural phase transition precedes SCO. The non-magnetic structural transformation is accompanied by reorganization of weak intermolecular interactions and shift of 2D layers with respect to each other. Surprisingly, an analog [Fe(bbtr)3](BF4)2, does not exhibit in cooling mode neither thermally SCO nor structural phase transition [2]. To clarify the role of structural phase transition on SCO we have performed structural modifications by exchanging the kind of anions and/or metal ions. An exchange of perchlorate on triflate anion involves deeper structural changes. A topology of the polymeric layer remains the same, but the SCO is shifted to higher temperature and structural phase transition is not observed. The studies of isostructural zinc(II) analogs confirmed the crucial role of anion in the occurrence of non-magnetic structural phase transition. The [Zn(bbtr)3](ClO4)2 exhibites P-3 -> P-1 structural phase transition which is not present in tetrafluoroborate analog [2]. We expand studies on other hexacoordinating metal(II) ions. Reactions between manganese(II) or cadmium(II) perchlorates and bbtr in acetonitrile lead to [M(bbtr)3](ClO4)2 (M=Mn, Cd) complexes. Single crystal X-ray diffraction studies revealed that both compounds create a 2D polymeric networks. The temperature dependence of lattice parameters for these complexes showed that, in contrast to [Fe(bbtr)3](ClO4)2 and [Zn(bbtr)3](ClO4)2 systems, the structural phase transition is not present. This work was funded by the Polish National Science Centre Grant No. DEC-2011/01/B/ST5/06311.

APA, Harvard, Vancouver, ISO, and other styles

41

Oyarzabal, Itziar, Estitxu Echenique-Errandonea, Eider San Sebastián, Antonio Rodríguez-Diéguez, José Manuel Seco, and Enrique Colacio. "Synthesis, Structural Features and Physical Properties of a Family of Triply Bridged Dinuclear 3d-4f Complexes." Magnetochemistry 7, no. 2 (February 5, 2021): 22. http://dx.doi.org/10.3390/magnetochemistry7020022.

Full text

Abstract:

New dinuclear MII-LnIII complexes of general formulas [Cu(µ-L)(µ-OAc)Ln(NO3)2]·CH3CN·H2O (LnIII = Gd (1), Tb (2), Dy (3) and Er (4)), [Ni(CH3CN)(µ-L)(µ-OAc)Ln(NO3)2]·CH3CN (LnIII = Nd (5), Gd (6), Tb (7), Dy (8), Er (9) and Y (10)) and [Co(CH3CN)(µ-L)(µ-OAc)Ln(NO3)2]·CH3CN (LnIII = Gd (11), Tb (12), Dy (13), Er (14) and Y (15)) were prepared from the compartmental ligand N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromo-benzyl)ethylenediamine (H2L). In all these complexes, the transition metal ions occupy the internal N2O2 coordination site of the ligand, whereas the LnIII ions lie in the O4 external site. Both metallic ions are connected by an acetate bridge, giving rise to triple mixed diphenoxido/acetate bridged MIILnIII compounds. Direct current (dc) magnetic measurements allow the study of the magnetic exchange interactions between the 3d and 4f metal ions, which is supported by density functional theory (DFT) theoretical calculations for the GdIII-based counterparts. Due to the weak ferromagnetic exchange coupling constants obtained both experimentally and theoretically, the magneto-thermal properties of the less anisotropic systems (compounds 1 and 6) are also studied. Alternating current (ac)magnetic measurements reveal the occurrence of slight frequency dependency of the out-of-phase signal for complexes 8, 9 and 13, while complex 15 displays well-defined maximums below ~6 K.

APA, Harvard, Vancouver, ISO, and other styles

42

Childs, Bradley J., Marcia L. Scudder, Donald C. Craig, and Harold A. Goodwin. "Structural and Electronic Properties of the Iron(II) and Nickel(II) Bis(ligand) Complexes of 6-(5-Methyl-1,2,4-oxadiazol-3-yl)-2,2′-bipyridine— a Terpyridine-Based Tridentate." Australian Journal of Chemistry 52, no. 7 (1999): 673. http://dx.doi.org/10.1071/ch98153.

Full text

Abstract:

Iron(II) and nickel(II) bis(ligand) complexes of 6-(5-methyl-1,2,4-oxadiazol-3-yl)-2,2′-bipyridine (L) are described. The ligand field in the iron complex is close to that at the singlet ( 1 A1) ? quintet ( 5 T2) crossover and magnetic and Mössbauer spectral evidence indicates that a spin transition occurs in salts of the iron complex but is centred above room temperature. The structures of [FeL2] [CF3SO3]2.CH3CN and [NiL2] [BF4]2.CH3CN were determined and both are very similar to the structures of the corresponding terpyridine complexes. Spectroscopic data indicate that for the iron complex π-interaction between the metal and the ligand is less than that in the terpyridine system. [FeL2] [CF3SO3]2.CH3CN is monoclinic, space group P 21/c; a 8 . 232(5), b 25 . 273(10), c 17 . 306(10) Å, β 92 . 37(3)°, Z 4; [NiL2] [BF4]2.CH3CN is monoclinic, space group P 21/c; a 8 . 136(2), b 17 . 558(2), c 23 . 783(7) Å, β 109 . 32(1)°, Z 4.

APA, Harvard, Vancouver, ISO, and other styles

43

Selyutina, Olga Yu, Simon V. Babenko, Irina A. Slepneva, Nikolay E. Polyakov, and George J. Kontoghiorghes. "Increased Free Radical Generation during the Interaction of a Quinone-Quinoline Chelator with Metal Ions and the Enhancing Effect of Light." Pharmaceuticals 16, no. 8 (August 8, 2023): 1116. http://dx.doi.org/10.3390/ph16081116.

Full text

Abstract:

Schiff bases and similar molecules forming metal complexes may cause redox effects, which may also be influenced by light. Anthraquinones such as doxorubicin and idarubicin are widely used antitumor agents, which can generate reactive oxygen species (ROS), stimulated by both the presence of iron and copper ions and also by light. The generated ROS can cause DNA scission, cell membrane oxidation, and many other toxic effects. The redox activity of the quinone-quinoline chelator 2-phenyl-4-(butylamino)naphtho [2,3-h]quinoline-7,12-dione (Q1) was investigated in the presence of iron, copper, and zinc. The influence of light in these interactions was also examined. The chemically induced dynamic nuclear polarization (CIDNP), nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) methods were used to elucidate the molecular changes and ROS generation effects of the Q1 metal interactions. A model electron transfer reaction system between 1,4-dihydropyridine and Q1 was utilized to demonstrate that the chelate complexes of Q1 with both Fe(III) and Cu(II) ions were more redox active than Q1 itself. Similarly, CIDNP and NMR data showed that the concentration dependence of the free radicals yield is much higher in the presence of Fe(III) and Cu(II) ions, in comparison to Zn(II), and also that it increased in the presence of light. These findings underline the role of transition metal ions and Q1 in cyclic redox chain reactions and increase the prospect of the development of copper- and iron-based chelating agents, including Q1 and its derivatives, for anticancer therapy. Furthermore, these findings also signify the effect of light on enhancing ROS formation by Q1 and the prospect of utilizing such information for designing target specific anticancer drugs for photodynamic therapy.

APA, Harvard, Vancouver, ISO, and other styles

44

KARAKAS, ASLI, AYHAN ELMALI, YASEMIN YAHSI, and HULYA KARA. "THIRD-ORDER NONLINEAR OPTIC AND OPTICAL LIMITING PROPERTIES OF A MN(III) TRANSITION METAL COMPLEX." Journal of Nonlinear Optical Physics & Materials 16, no. 04 (December 2007): 505–18. http://dx.doi.org/10.1142/s0218863507003858.

Full text

Abstract:

N,N′-bis(5-bromosalicylidene)propane-1,2-diamine-O,O′,N,N′)-manganese(III) chloride transition metal complex has been synthesized and characterized by elemental analysis and UV-vis spectroscopy. Its crystal structure has been determined using X-ray diffraction analysis. To provide an insight into the optical limiting (OL) behavior of the title compound, the third-order nonlinear optical (NLO) properties, one-photon absorption (OPA) and two-photon absorption (TPA) characterizations have been theoretically investigated by means of the time-dependent Hartree–Fock (TDHF), AM1 and configuration interaction (CI) methods, respectively. According to ab initio calculation results, the examined molecule exhibits second hyperpolarizabilities (γ) with non-zero values at the positions of TPA peaks, implying microscopic third-order optical nonlinearity. The maximum OPA wavelengths recorded by linear optical experiment and quantum mechanical computations are estimated in the UV region to be shorter than 400 nm, showing good optical transparency to the visible light. The TPA cross-sections (δ(ω)) at [Formula: see text] values indicate that the synthesized compound might possess OL phenomena, which are in accord with the experimental observations on the manganese complexes in the literature.

APA, Harvard, Vancouver, ISO, and other styles

45

Zapata-Rivera, Jhon, and Carmen Calzado. "Light-Induced Control of the Spin Distribution on Cu–Dithiolene Complexes: A Correlated Ab Initio Study." Molecules 24, no. 6 (March 19, 2019): 1088. http://dx.doi.org/10.3390/molecules24061088.

Full text

Abstract:

Metal dithiolene complexes—M(dmit)2—are key building blocks for magnetic, conducting, and optical molecular materials, with singular electronic structures resulting from the mixing of the metal and dmit ligand orbitals. Their use in the design of magnetic and conducting materials is linked to the control of the unpaired electrons and their localized/delocalized nature. It has been recently found that UV–Vis light can control the spin distribution of some [Cu(dmit)2]−2 salts in a direct and reversible way. In this work, we study the optical response of these salts and the origin of the differences observed in the EPR spectra under UV–Vis irradiation by means of wave function-based quantum chemistry methods. The low-lying states of the complex have been characterized and the electronic transitions with a non-negligible oscillator strength have been identified. The population of the corresponding excited states promoted by the UV–Vis absorption produces significant changes in the spin distribution, and could explain the changes observed in the system upon illumination. The interaction between neighbor [Cu(dmit)2]−2 complexes is weakly ferromagnetic, consistent with the relative orientation of the magnetic orbitals and the crystal packing, but in disagreement with previous assignments. Our results put in evidence the complex electronic structure of the [Cu(dmit)2]−2 radical and the relevance of a multideterminantal approach for an adequate analysis of their properties.

APA, Harvard, Vancouver, ISO, and other styles

46

Du, Dongying, Junsheng Qin, Shunli Li, Yaqian Lan, Xinlong Wang, and Zhongmin Su. "3d - 4f Heterometallic Complexes for the Construction of POM-based Inorganic - Organic Hybrid Compounds: from Nanoclusters to One-Dimensional Ladder-Like Chains." Australian Journal of Chemistry 63, no. 9 (2010): 1389. http://dx.doi.org/10.1071/ch10047.

Full text

Abstract:

Three polyoxometalate-based inorganic–organic hybrid compounds, namely nanoclusters [Cu(en)2H2O]3[(α-SiW11O39)Nd(H2O)(η2,μ-1,1)-CH3COO]·3.5H2O (1) and [Cu(en)2H2O]3[(α-SiW11O39)Sm(H2O)(η2,μ-1,1)-CH3COO]·3H2O (2), and 1D H2[Cu(en)2H2O]8[Cu(en)2]3[{(α-SiW11O39)Ce(H2O)(η2,μ-1,1)-CH3COO}4]·22H2O (3) (en = 1,2-ethylenediamine) have been isolated. 1 and 2 are isomorphic and consist of [(α-SiW11O39)Ln(H2O)(η2,μ-1,1)-CH3COO]6– polyanions modified by [Cu(en)2H2O]2+ fragments. In 3, [Cu(en)2H2O]2+ are grafted on [(α-SiW11O39)Ce(H2O)(η2,μ-1,1)-CH3COO]6– polyanions and further connected by [Cu(en)2]2+ groups, representing the first example in polyoxometalate chemistry of a 1D ladder-like polyanion chain consisting of monovacant Keggin-type polyanions, lanthanide complexes and transition metal complexes. In these compounds, copper complexes coordinate to not only terminal O atoms but also bridging O atoms of the polyanions. Magnetic studies of 1 and 3 reveal weak antiferromagnetic interactions exist in them.

APA, Harvard, Vancouver, ISO, and other styles

47

Allerdt, Andrew, Hasnain Hafiz, Bernardo Barbiellini, Arun Bansil, and Adrian E. Feiguin. "Many-Body Effects in FeN4 Center Embedded in Graphene." Applied Sciences 10, no. 7 (April 7, 2020): 2542. http://dx.doi.org/10.3390/app10072542.

Full text

Abstract:

We introduce a computational approach to study porphyrin-like transition metal complexes, bridging density functional theory and exact many-body techniques, such as the density matrix renormalization group (DMRG). We first derive a multi-orbital Anderson impurity Hamiltonian starting from first principles considerations that qualitatively reproduce generalized gradient approximation (GGA)+U results when ignoring inter-orbital Coulomb repulsion U ′ and Hund exchange J. An exact canonical transformation is used to reduce the dimensionality of the problem and make it amenable to DMRG calculations, including all many-body terms (both intra- and inter-orbital), which are treated in a numerically exact way. We apply this technique to FeN 4 centers in graphene and show that the inclusion of these terms has dramatic effects: as the iron orbitals become single occupied due to the Coulomb repulsion, the inter-orbital interaction further reduces the occupation, yielding a non-monotonic behavior of the magnetic moment as a function of the interactions, with maximum polarization only in a small window at intermediate values of the parameters. Furthermore, U ′ changes the relative position of the peaks in the density of states, particularly on the iron d z 2 orbital, which is expected to affect the binding of ligands greatly.

APA, Harvard, Vancouver, ISO, and other styles

48

Kubicki, Marek M., Jean-Yves Le Gall, René Kergoat, and Luiz C. Gomes De Lima. "Cyclopentadienyl complexes with transition metal – main group metal bonds. VII. 207Pb and 95Mo nuclear magnetic resonance studies on molybdenum and tungsten complexes [(η5-C5H5)(CO)3M]nPbR4−n (n = 1, R = Me, Et, Ph; n = 2, R = Ph)." Canadian Journal of Chemistry 65, no. 6 (June 1, 1987): 1292–97. http://dx.doi.org/10.1139/v87-216.

Full text

Abstract:

Nuclear magnetic resonance measurements of metallic nuclei (δ 207Pb, δ 95Mo, and 1J(W–Pb)) have been carried out on dimetallic Cp(CO)3MPbR3 (M = Mo, W; R = Me, Et, Ph) and trimetallic [Cp(CO)3M]2PbPh2 (M = Mo, W) complexes. 207Pb chemical shifts increase in the sequence PbEt3 < PbMe3 < PbPh3 and are observed at higher fields in the tungsten compounds than in the molybdenum ones. It is suggested that both paramagnetic and diamagnetic contributions determine the overall shielding of lead, and that the higher field resonances of 207Pb in the case of W–Pb compounds are due to an efficacious operation of the Z/r dependent diamagnetic term (higher atomic number Z of tungsten and roughly the same Mo–Pb and W–Pb distances resulting from the 4f level induced lanthanide contraction). 95Mo chemical shifts (−1838 to −2007 ppm) lie in the region typical of the molybdenum – main group metal bonded complexes but at lower fields than in the corresponding Mo–Sn compounds. It is concluded from this observation that the Z/r dependent diamagnetic contribution does not operate efficaciously for 95Mo shieldings, which are hence primarily dominated by the paramagnetic term. The nature of metal–metal interactions is discussed.

APA, Harvard, Vancouver, ISO, and other styles

49

ZHANG, YI QUAN, CHENG LIN LUO, and ZHI YU. "MAGNETIC COUPLING CONSTANTS AND SPIN DENSITY DISTRIBUTIONS FOR CYANO-BRIDGED Gd(III)-Fe(III) AND Gd(III)-Cr(III) COMPOUNDS: BROKEN-SYMMETRY AND DENSITY FUNCTIONAL THEORY CALCULATIONS." International Journal of Modern Physics B 19, no. 15n17 (July 10, 2005): 2538–43. http://dx.doi.org/10.1142/s0217979205031286.

Full text

Abstract:

Magnetic coupling constants J for the complete structures of [ Gd(capro) 2( H 2 O )4 Cr(CN) 6]• H 2 O (capro represents caprolactam) (a) and trans-[ Fe(CN) 4(μ- CN )2 Gd ( H 2 O )4 (bpy) ]•4 H 2 O •1.5 bpy (b) have been calculated using hybrid density functional theory (DFT) B3LYP combined with a modified broken symmetry approach (BS). The calculated J value of -0.24 cm-1 for a is very close to the experimental -0.33 cm-1. They both show the antiferromagnetic interaction between Gd(III) and Cr(III) . For b, although the sign of the calculated J value of 4.24 cm-1 is different from that of the experimental -0.38 cm-1, the two values both show the weak magnetic coupling interaction between Gd(III) and Fe(III) . The spin density distributions are discussed on the basis of Mulliken population analysis. For complexes a and b, both transition metal ( Fe(III) or Cr(III) ) and rare earth Gd(III) display a spin polarization effect on the surrounding atoms, where a counteraction of the opposite polarization effects leads to a low spin density on the bridging ligand C1N1 . For the compounds Gd(III) - Cr(III) (a) and Gd(III) - Fe(III) (b) in the HS states, Cr(III) has stronger spin polarization influence on the bridging atoms than Fe(III) even causing the positive spin population on the bridging atom N1 .

APA, Harvard, Vancouver, ISO, and other styles

50

Möbius, Klaus, Wolfgang Lubitz, Nicholas Cox, and Anton Savitsky. "Biomolecular EPR Meets NMR at High Magnetic Fields." Magnetochemistry 4, no. 4 (November 6, 2018): 50. http://dx.doi.org/10.3390/magnetochemistry4040050.

Full text

Abstract:

In this review on advanced biomolecular EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR regarding the measurement of interactions and dynamics of large molecules embedded in fluid-solution or solid-state environments. Our focus is on the characterization of protein structure, dynamics and interactions, using sophisticated EPR spectroscopy methods. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed the limits of EPR spectroscopy to new horizons reaching millimeter and sub-millimeter wavelengths and 15 T Zeeman fields. Expanding traditional applications to paramagnetic systems, spin-labeling of biomolecules has become a mainstream multifrequency approach in EPR spectroscopy. In the high-frequency/high-field EPR region, sub-micromolar concentrations of nitroxide spin-labeled molecules are now sufficient to characterize reaction intermediates of complex biomolecular processes. This offers promising analytical applications in biochemistry and molecular biology where sample material is often difficult to prepare in sufficient concentration for NMR characterization. For multifrequency EPR experiments on frozen solutions typical sample volumes are of the order of 250 μL (S-band), 150 μL (X-band), 10 μL (Q-band) and 1 μL (W-band). These are orders of magnitude smaller than the sample volumes required for modern liquid- or solid-state NMR spectroscopy. An important additional advantage of EPR over NMR is the ability to detect and characterize even short-lived paramagnetic reaction intermediates (down to a lifetime of a few ns). Electron–nuclear and electron–electron double-resonance techniques such as electron–nuclear double resonance (ENDOR), ELDOR-detected NMR, PELDOR (DEER) further improve the spectroscopic selectivity for the various magnetic interactions and their evolution in the frequency and time domains. PELDOR techniques applied to frozen-solution samples of doubly spin-labeled proteins allow for molecular distance measurements ranging up to about 100 Å. For disordered frozen-solution samples high-field EPR spectroscopy allows greatly improved orientational selection of the molecules within the laboratory axes reference system by means of the anisotropic electron Zeeman interaction. Single-crystal resolution is approached at the canonical g-tensor orientations—even for molecules with very small g-anisotropies. Unique structural, functional, and dynamic information about molecular systems is thus revealed that can hardly be obtained by other analytical techniques. On the other hand, the limitation to systems with unpaired electrons means that EPR is less widely used than NMR. However, this limitation also means that EPR offers greater specificity, since ordinary chemical solvents and matrices do not give rise to EPR in contrast to NMR spectra. Thus, multifrequency EPR spectroscopy plays an important role in better understanding paramagnetic species such as organic and inorganic radicals, transition metal complexes as found in many catalysts or metalloenzymes, transient species such as light-generated spin-correlated radical pairs and triplets occurring in protein complexes of photosynthetic reaction centers, electron-transfer relays, etc. Special attention is drawn to high-field EPR experiments on photosynthetic reaction centers embedded in specific sugar matrices that enable organisms to survive extreme dryness and heat stress by adopting an anhydrobiotic state. After a more general overview on methods and applications of advanced multifrequency EPR spectroscopy, a few representative examples are reviewed to some detail in two Case Studies: (I) High-field ELDOR-detected NMR (EDNMR) as a general method for electron–nuclear hyperfine spectroscopy of nitroxide radical and transition metal containing systems; (II) High-field ENDOR and EDNMR studies of the Oxygen Evolving Complex (OEC) in Photosystem II, which performs water oxidation in photosynthesis, i.e., the light-driven splitting of water into its elemental constituents, which is one of the most important chemical reactions on Earth.

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Magnetic Interaction - Transition Metal Complexes'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles