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

• Anionic cis-dioxidovanadium(V) complexes with protonated organic base as counter ion have been synthesized.
• The molecules have hydrogen bonded oligomeric structures in the solid state.
• In acetonitrile, they undergo proton-coupled photo-induced reduction.
• The reduced products display 15-line EPR and inter-valence charge-transfer bands.
• Results confirm the formation of μ-oxidodivanadium(IV/V) compounds during the photo-reduction.

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.

cis-Dioxidovanadium(V) compounds (BH)[VVO2L] of dithiocarbazate based tridentate biprotic Schiff-base ligands (H2L) are photo-reactive in dry acetonitrile solution and undergo proton-coupled one-electron reduction when exposed to visible light to generate μ-oxido mixed-oxidation divanadium(IV/V) compounds (BH)[LOVV-(μ-O)-VIVOL] showing characteristic 15-line EPR spectra in solution at room temperature.Figure optionsDownload as PowerPoint slide