Transition-metal complexes of biuret and related ligands. Part I. Biuret complexes of some bivalent metal ions

Abstract

The preparations of several complexes formed between biuret and transition-metal ions in both netural and alkaline solution are described. The mode of co-ordination of biuret in these complexes has been established by infrared spectral measurements, complexes whose structures have been completely established by X-ray analysis being used as standards. Ultraviolet and visible spectra and magnetic susceptibility measurements have been obtained on the solid complexes, enabling comparisons of ligand field strengths between different types of co-ordination for biuret to be made. The purple copper(II) complex isolated from alkaline solution is believed to have a dimeric structure K₂[(Cu(NH·CO·NH·CO·NH)OH)₂],4H₂O, with two hydroxide bridges linking the copper atoms. A super-exchange mechanism through these hydroxide bridges is postulated to account for the lowering of the magnetic moment of the copper(II) ions to 1·10 Bohr magnetons at room temperature.