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

Abstract

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.