Complex formation between transition metals and 2-pyrrolidone-5-hydroxamic acid

Complexes of cobalt(II), nickel(II) and copper(II) with 2-pyrrolidone-5-hydroxamic acid (HL) have been investigated by the combined pH-spectral titration method at 25 +/- 0.1 degreesC in aqueous medium of 0.2 M ionic strength. Cobalt(II) and nickel(II) form [ML](+), [ML2] and [ML2H-1](-) complexes with HL, while in the case of copper(II) mononuclear [CuL](+) and dinuclear [Cu2L2H-2] species are present. The formation constants obtained and the possible binding modes for the complexes in aqueous solution are discussed. H-1 NMR, IR and EPR measurements have furnished additional information on the nature of binding in the complexes formed.