V. V. Lukov

Magnetic exchange in Bi- and polynuclear complexes of transition metals with hydrazones and azomethines

Magnetic exchange data for bi- and polynuclear complexes of transition metals with hydrazones, Schiff bases, oximes, and related systems were generalized and systematized. A correlation between the electronic and geometrical structures of the complexes and characteristic exchange effects was discussed. A systematic analysis of magnetostructural correlations in such complexes was performed.

Binuclear copper(II) and oxovanadium(IV) complexes with 2,6-diformyl-4- tert -butylphenol- bis -(1′-phthalazinylhydrazone). Synthesis, properties and quantum chemical study

Four binuclear transition metal complexes: [Cu2L(μ-OCH3)] · CH3OH, [Cu2H2L(μ-Cl)Cl2] · (CH3OH), [Cu2H2L(μ-Br)Br2] · (CH3OH), [(VO)2H2L(μ-Cl)]Cl2 · (CH3OH) were synthesized by reaction of the Robson-type binucleating ligand H3L (2,6-diformyl-4-tert-butylphenol-bis-(1′-phthalazinylhydrazone)) with Cu(II) acetate, CuCl2, CuBr2 and VOCl2, correspondingly. IR and ESR spectra, elemental analysis, conductivity measurements, magnetochemical study and DFT calculations were used to characterize the ligand and isolated complexes. The ligand is a NNONN donor and its degree of deprotonation varies with the metal salt used for reaction (triply deprotonated form L−3 is observed in reaction with copper(II) acetate, while monodeprotonated form H2L− is found in complexes obtained from metal halides). All complexes contain an endogenous phenoxide bridge and an exogenous methoxide, chloride or bromide bridge. Magnetic data reveal existence of antiferromagnetic interactions between the metal ions (experimental 2J values are −700, −73, −50 and −190 cm−1, correspondingly). Broken symmetry approach at the UB3LYP/6-31G(d) level was used to theoretically calculate spin-spin coupling between metal centers. Obtained values −570, −62, −53 and −214 cm−1 are rather close to experimental ones and reproduce their counterrelation. Spin density distribution in the singlet and triplet states of the complexes is discussed.

Magnetochemistry of Homo- and Heterobinuclear Complexes with Bis(hydrazones) of 2,6-Diformyl-4-R-Phenols

Data on the magnetochemical properties of binuclear copper(II) complexes with different bishydrazone ligands prepared from 2,6-diformylphenol are surveyed. An attempt to systematize the investigation results by elucidating the magnetostructural dependences that relate the strength of exchange interaction to the structure of the binuclear complex is made. Experimental and theoretical data are presented demonstrating the dependence of the exchange interaction strength on both the geometry of the exchange fragment and the nearest environment and the nature of the nonbridging donor atoms coordinated directly by the metal.

Transition metal complexes with 2-(N-tosylamino)benzaldehyde 1-phthalazinylhydrazone

Abstract2-(N-Tosylamino)benzaldehyde 1-phthalazinylhydrazone (H2L) and its complexes with Cu(II), Ni(II), and Mn(II) were obtained. The acid-basic properties of the hydrazone were studied using potentiometry and spectrophotometry. The experimental data were compared with the results of quantum-chemical DFT calculations. The structure of the binuclear complex [Cu2L2] was determined using X-ray diffraction. The broken symmetry approach was used to calculate the exchange coupling constant of the copper ions.

Influence of structural factors on the magnetic properties of the binuclear copper complexes with salicylaldehyde hydrazone and bis(hydrazone)-2,6-diformylphenol: Quantum-chemical calculations

The structures and magnetic properties of the binuclear copper complexes of salicylaldehyde mono- and bis(hydrazone) derivatives were studied by the quantum-chemical density functional theory (B3LYP/6-311++g(d,p)) using the broken-symmetry technique. The change in the degree of deprotonation of the ligands was found to exert an insignificant effect on the magnetic properties, whereas the coordination of solvent molecules substantially weakened the antiferromagnetic interaction.

Influence of the bridging coordination of DMSO on the exchange interaction character in the binuclear copper(II) complex with the nonsymmetrical exchange fragment

The binuclear copper(II) complex [Cu2L(CH3COO)] (I), where L3− is the azomethine trianion based on 3-methyl-4-formyl-1-phenylpyrazol-5-one and 1,3-diaminopropan-2-ol, and its DMSO adduct (II) in which the DMSO molecule acts as an additional bridging ligand are synthesized. The structure of complex II is determined by X-ray diffraction analysis, and the structure parameters of the coordination unit of complex I are determined by EXAFS spectroscopy. The μ2-coordination of the DMSO molecule in compound II results in a change in the sign of the exchange interaction parameter. In complex I, the antiferromagnetic exchange interaction (2J = −169 cm−1) occurs between the copper(II) ions. The exchange interaction of the ferromagnetic type (2J = 174 cm−1) is observed in complex II. The quantum-chemical calculations of the magnetic exchange parameters by the density functional theory method show that the role of the DMSO molecule as a switch of the exchange interaction character is exclusively the stabilization of the “broken” conformation of the metallocycles.

Crystal structure of 2-acetylbenzimidazole 1′-phthalazinylhydrazone

Using X-ray diffraction study of acetylbenzimidazole 2-acetylbenzimidazole 1′-phthalazinylhydrazone we confirmed that this compounds exists as the phthalazonehydrazone tautomer, as was suggested earlier on the basis of IR and NMR spectroscopy and quantum-chemical calculations.

Mono- and Binuclear Copper(II) Metal Chelates with 3,5-Di(tert-butyl)salicylaldehyde Acylhydrazones

Some new mono- and binuclear complexes of copper(II) acetate, nitrate, and perchlorate with acylhydrazones of substituted salicylaldehyde derivatives containing bulky tert-butyl substituents are synthesized. The structure and properties of the complexes isolated are shown to be determined by both the structural features of the ligand systems and by the nature of the acido ligands. The exchange parameters 2J ranging from –108 to –125 cm–1 are calculated for the binuclear copper(II) metal chelates.

Peculiarities of magnetic exchange in bi- and tetranuclear copper(II) complexes with organic ligands based on 1,3-diaminopropan-2-ol

The main types of mechanisms of exchange interactions are considered in the review in the framework of experimental and theoretical analyses. The electronic and geometric factors that exert a determining effect on the magnetic properties of the bi- and tetranuclear complexes of transition metals based on hydrazones and azomethines of 1,3-diaminopropan-2-ol are revealed.

Tetranuclear Copper(II) Complex with N,N′-bis(2-N-Tosylaminobenzylidene)-1,3-Diaminopropan-2-ol: Crystal structure and magnetic properties

Tetranuclear copper(II) complex, [Cu4L2(OOCCH2COO)], where L is triply deprotonated bis-N,N′-(2-N-tosylaminobenzylidene)-1,3-diaminopropan-2-ol, in which two binuclear fragments are linked by the malonate dianion, is synthesized. The exchange interaction in the binuclear clusters is shown to be antiferromagnetic (2J = −59 cm−1), whereas the intercluster interaction is ferromagnetic (zJ’ = 7.5 cm−1). The structure of the DMSO solvate of the complex is determined by X-ray diffraction analysis.