Synthesis and structural characterization of copper(II) and vanadium(V) complexes of pyridyl/pyrimidyl–pyrazole derived Schiff base ligands – Metal specific adjustment of ligand binding mode

Two mononuclear copper(II) complexes [Cu(L1)ClO4] (1), [Cu(L2)ClO4] (3) and two mononuclear vanadium(V) complexes [{VO(L1)(OCH3)(CH3OH)}{VO(L1)(OCH3)}] (2) and [VO(L2) (OCH3)(CH3OH)] (4) have been synthesized using two Schiff base ligands HL1 [N′-(2-hydroxybenzylidene)-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazide] and HL2 [1-(4,6-dimethylpyrimidin-2-yl)-N′-(2-hydroxybenzylidene)-5-methyl-1H-pyrazole-3-carbohydrazide]. These two similar ligands HL1 and HL2 in their ‘ketoimine’ form function as mononegative NNNO tetradentate ones towards the Cu(II) centre forming square planar part of the square pyramidal geometry. Where as the same ligands in their ‘imineol’ form behave as binegative ONO tridentate ones to form their V(V) analogues. In the asymmetric unit of 2, there are two independent V(V) complex molecules differing in their conformations as well as in coordination environment – octahedral V(V) in ‘unit A’ is hexa-coordinated while that in ‘unit B’ being penta-coordinated is square pyramidal. Vanadium atom in 4 is in octahedral geometry with NO5 chromophore. The ligands HL1 and HL2 have been synthesized for the first time in our laboratory and characterized by X-ray crystallography and spectroscopy. The complexes (1, 2 and 4) are also characterized by X-ray crystallography, spectroscopic and electrochemical studies.

Two Schiff base ligands HL1 and HL2 form two penta-coordinated square pyramidal Cu(II) complexes (1 and 3) and two V(V) complexes (2 and 4). The asymmetric unit of 2, being comprised of two independent molecules has an square pyramidal and one distorted octahedral V(V) units differing in their conformation. The vanadium(V) atom in 4 is in distorted octahedral geometry with NO5 chromophore.Figure optionsDownload as PowerPoint slide