Adduct Formation between Alkali Metal Ions and Anionic LVVO2- (L2- = Tridentate ONS Ligands) Species: Syntheses, Structural Investigation, and Photochemical Studies

Syntheses of alkali metal adducts [LVO2M(H2O)n] (1-7) (M = Na+, K+, Rb+, and Cs+; L = L1-L3) of anionic cis-dioxovanadium(V) species (LVO2-) of tridentate dithiocarbazate-based Schiff base ligands H2L (S-methyl-3-((5-(R-2-hydroxyphenyl))methyl)dithiocarbazate, R = H, L = L1; R = NO2, L = L2; R = Br, L = L3) have been reported. The LVO2- moieties here behave like an analogue of carboxylate group and have displayed interesting variations in their binding pattern with the change in size of the alkali metal ions as revealed in the solid state from the X-ray crystallographic analysis of 1, 3, 6, and 7. The compounds have extended chain structures, forming ion channels, and are stabilized by strong Coulombic and hydrogen-bonded interactions. The number of coordinated water molecules in [LVO2M(H2O)n] decreases as the charge density on the alkali metal ion decreases (n = 3.5 for Na+ and 1 for K+ and Rb+, while, for Cs+, no coordinated water molecule is present). In solution, compounds 1-7 are stable in water and methanol, while in aprotic solvents of higher donor strengths, viz. CH3CN, DMF and DMSO, they undergo photoinduced reduction when exposed to visible light, yielding green solutions from their initial yellow color. The putative product is a mixed-oxidation (-oxo)divanadium(IV/V) species as revealed from EPR, electronic spectroscopy, dynamic 1H NMR, and redox studies.