Vanadium(IV) and oxovanadium(IV) complexes of hydroxamic acids and related ligands.

Complex formation between oxovanadium(IV) and a series of hydroxamic or hydroxamic-like ligands (acetohydroxamic, benzohydroxamic, 2-hydroxypyridine-N-oxide and N-phenyl-benzohydroxamic acids) has been investigated in solution by EPR spectroscopy. VO(IV) complexes involving the ligand-to-metal molar ratio of 2:1 have also been isolated in the solid state. The results show that the simple hydroxamic ligands (acetohydroxamic and benzohydroxamic acids) can undergo two deprotonation processes and thus act as either hydroxamato(1-) or hydroximato(2-) ligands. A similar dissociation pattern is not possible for N-phenyl-benzohydroxamic acid and the hydroxamic-like ligand 2-hydroxypyridine-N-oxide, which are able to yield only a hydroxamato(1-) coordinating anion. All the ligands form hexa-coordinate tris-chelated complexes of V(IV) after displacing the oxo group from VO(IV).