Phosphate Complexation of Oxovanadium(IV)-Evidence of Bidentate Chelation of Ortophosphate

The oxovanadium(IV) complexes formed in aqueous solutions by ethylenediaminetetraacetic (EDTA), N-(2-hydroxyethyl)ethylenediaminetriacetic (HEDTA), ethylenebis(oxyethylenenitrilo(tetraacetic (EGTA), trans-(1,2-cyclohexylenedinitrilo)tetraacetic (CDTA), ethylenediamine-N,N?-diacetic (EDDA), nitrilotriacetic (NTA), iminodiacetic (IDA), N-methyliminodiacetic (MIDA), ethylenediamine-N,N?-dipropionic (EDDP) and N,N?-ethylenedianthranilic (EDA) acids have been studied by EPR and electronic absorption spectroscopy. The species taking part in the complex formation processes have been identified and structures proposed by previous equilibrium studies have been examined and discussed on the basis of the spectroscopic data. In particular, hydrolysis has been found to yield mononuclear and dinuclear hydroxo species. The dinuclear di-?-hydroxo species formed by iminodiacetate-like ligands exhibit EPR spectra indicative of the triplet state and have been assigned as involving intermolecular carboxylate binding and hydroxyl bridges. EPR-silent di-?-hydroxo complexes have been substantiated by the intensity loss of the EPR signals.