Proton Electron Nuclear Double Resonance Study of Oxovanadium(IV) Complexes of o-Diphenolic Ligands

The vanadium(IV) complexes of catechol, 3,4-di hydroxybenzoic acid, and naphthalene-2,3-diol, in water or D,O solution, have been studied by 'H electron nuclear double resonance (ENDOR) spectroscopy at 11 0 K. The spectra show prominent peaks which are due to ring protons adjacent to metal-bound phenolate groups, together with resonances which have contributions from more distant protons. On the whole, the 'H ENDOR patterns of the studied complexes may be satisfactorily assigned using the structural data for potassium bis(catecholato)oxovanadate(IV) and thus may be considered as diagnostic of vanadium(IV)-phenolate co-ordination. The presence of outer-sphere water molecules has also been detected in aqueous solution.