Oxovanadium(IV) and -(V) Complexes of Dithiocarbazate-Based Tridentate Schiff Base Ligands: Syntheses, Structure, and Photochemical Reactivity of Compounds Involving Imidazole Derivatives as Coligands

The tridentate dithiocarbazate-based Schiff base ligands HgL (S-methyl-3-((5-R-2-hydroxyphenyl)methyl)dithiocarbazate, R = NC)2, L = L R = Br, L == L react with [V0(acac)2] in the presence of imidazole derivatives as coligands to form oxovanadium(IV) and cis-dioxovanadium(V) complexes. With benzimidazole and A/-methylimidazole, the products are oxovanadium(IV) complexes, viz. [VOLBzImO.SCHsCN (la) and [VOL(A/-Melm)2] (L = L 1b; L = L, 1c), respectively. In both 1a,b, the 0 and S donor atoms of the tridentate ligand are cis to the terminal oxo group (in the "equatorial" plane) and mutually trans, but the N donor atom is respectively cis and trans to the oxo atom, as revealed from X-ray crystallography. When imidazole or 4-methylimidazole is used as the ancillary ligand, the products obtained are water-soluble c/s-dioxovanadium(V) complexes [VOL(Rʹ-lmH)] (L = U and L Rʹ = H and Me, 2a-d). These compounds have zigzag chain structures in the solid state as confirmed by X-ray crystallographic investigations of 2a,d, involving an alternating array of LVC)2~ species and the imidazolium counterions held together by Coulombic interactions and strong hydrogen bonding. Complexes 2a-d are stable in water or methanoi. In aprotic solvents, viz. CHsCN, DMF, or DMSO, however, they undergo photochemical transformation when exposed to visible light. The putative product is a mixed-oxidation divanadium(IV/V) species obtained by photoinduced reduction as established by EPR, electronic spectroscopy, and dynamic H NMR experiments.