I. N. Shcherbakov

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.

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.

1'-Phthalazine Hydrazone of Diacetyl Monooxime and Its Complexes with Transition Metals: Physicochemical and Theoretical Study

Abstract1′-Phthalazine hydrazone of diacetyl monooxime and its Cu(II) and Ni(II) complexes were synthesized. The acid-base properties of the hydrazone were potentiometrically and spectrophotometrically studied, and quantum-chemical calculations of the ionization constants and the energies of possible tautomeric forms and conformations were performed. Complexes of copper(II) prepared by the reaction of the hydrazone with copper(II) acetate, chloride, and bromide were shown to have the dimeric structure with the bidentatebridging N-O-groups of the oxime fragment, whereas the copper(II) complex prepared from copper(II) nitrate, forms the dimer via the endocyclic nitrogen atoms of the phthalazine fragment.

Effect of the nature of non-bridging donor atoms on the structure and magnetic properties of binuclear copper(II) complexes with heterocyclic azomethyne ligands

Pyrazolate bridging binuclear copper(II) complex with a heterocyclic azomethyne ligand (a condensation product of 1,3-diaminopropanol-2 with 1-phenyl-3-methyl-4-formyl-5-mercaptopyrazole) is synthesized and structurally characterized. The structure of the complex is compared with the structure of its pyrazolone analogue. It is shown that for the 2J calculation the use of the previously optimized geometry rather than the geometry from the XRD data results in better agreement with the magnetochemical experiment.

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 and magnetic properties of the binuclear copper(II) complex based on 1,3-diaminopropan-2-ol N,N′-bis(3-formyl-5-tert-butylsalicylidene)

Abstract1,3-Diaminopropan-2-ol N,N′-bis(3-formyl-5-tert-butylsalicylidene) (H3L) and the binuclear copper(II) complex based on H3L, [Cu2L(CH3COO)] (I), are synthesized. The compounds are studied by IR and 1H NMR spectroscopies, magnetochemistry, and X-ray diffraction analysis. Compared to the copper(II) complexes with 1,3-diaminopropan-2-ol N,N′-bis(salicylidene), complex I is characterized by a substantial change in the structure resulting in weakening of the antiferromagnetic exchange interaction.

X-ray absorption spectroscopic and magneto-chemical analysis of the atomic structure of copper(II) complexes with diacetyl monoxime 1′-phthalazinyl hydrazone

The atomic structure of copper(II) complexes based on diacetyl monoxime 1′-phthalazinyl hydrazone is studied by XANES spectral analysis and magnetochemistry. The XANES spectra at the CuK-edge are measured in C24H24N10Cu2O2 and C24H24N10Cu2O2 complexes. The calculations of the CuK-XANES spectra of the complexes in question are performed for a few structural models based on the full-potential finite difference method. By low-temperature magnetochemistry magnetic exchange parameters are determined, and a quantum chemical simulation of the exchange interaction is carried out within the broken symmetry approximation. Based on a combined analysis of the XANES spectra and magnetic exchange parameters, the most probable structural models of C24H24N10Cu2O2 and C24H24N10Cu2O2 complexes are found.

Protolytic Properties of 8-Quinolylhydrazones of Substituted Salicylaldehydes and Physicochemical Properties of Their Copper(II) Complexes

Acid-base properties of hydrazones derived from 8-hydrazinoquinoline and substituted salicylaldehydes were studied. Under the experimental conditions, only the first step of ionization of the hydrazones is realized. The ionization constants were calculated quantum-chemically. Copper(II) complexes of these hydrazones, (HL)Cu(X)(CH3OH)n, were isolated (HL− is the monodeprotonated form of hydrazones, and X− is the acid residue). According to the data of elemental analysis, IR spectroscopy, conductometry, and magnetochemistry, the majority of the complexes have a binuclear structure. The copper(II) ions in the dimeric complex show antiferromagnetic exchange coupling. The ionization constants of the hydrazones and the exchange parameters strongly depend on the substituent in the salicylaldehyde moiety.

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.