Chemistry of anionic cis-dioxidovanadium(V) complexes containing protonated organic bases as counterion: Self-assembly, oligomerization and photoinduced reactivity

The tridentate dithiocarbazate-based Schiff base ligands H2L (S-methyl-3-((5-X-2-hydroxyphenyl)methyl)dithiocarbazate, X = H, L = L1; X = NO2, L = L2) react with [VIVO(acac)2] in acetonitrile solution under refluxing condition in the presence of an organic base or ammonium ion (added in moderate excess) as co-ligand to generate cis-dioxidovanadium(V) complexes viz. (NH4)[VVO2L2(H2O)] 1, (gunH)[VVO2L1] 2, (gunH)[VVO2L2] 3 and (cytH)[VVO2L1](cyt) 4 (gun = guanidine and cyt = cytosine). These compounds have oligomeric structures in the solid state as confirmed by X-ray crystallographic investigation, involving an alternating array of anionic [LVO2]− species and the BH+ counterion held together by Coulombic interactions and strong hydrogen bonding. These compounds are stable in methanol solution. In aprotic solvents of higher donor numbers, viz. CH3CN, DMF, or DMSO, these compounds undergo photo-induced transformation when exposed to visible light. The product obtained appears to be a μ-oxidodivanadium(IV/V) mixed-oxidation compound (BH)[LOVV-(μ-O)-VIVOL] as established by EPR, electronic spectroscopy in the NIR region, and dynamic 1H NMR spectroscopic studies.