The metal complexes of amino acids and their N-substituted derivatives—VI. The physical properties, i.r. spectra and normal coordinate analysis of bivalent metal complexes with dl-threonine

Abstract

Complexes of five bivalent metals with dl-threonine have been prepared and characterized by means of i.r. absorption, powder diffuse reflection, and electronic spectra, X-ray diffraction and magnetic susceptibility. The complexes appear to be of three distinct types. The first type includes ML 2· nH 2O (M = Ni, Cu, Zn; L = dl-threoninato anion), in which the ligand chelates metal ions through the nitrogen atom and the oxygen atom of the carboxylato group. Three species of copper(II) complexes have been prepared. They seem to be two trans forms and one cis form. MnCl 2(HL) 4·H 2O is a second type in which the metal is coordinated through the oxygen atom of the carboxyl group and chloride ions, but is not coordinated through the nitrogen atom. 2CdCl 2·HL·HCl·2H 2O is a third type, in which the metal is coordinated through only chloride ions. In order to assign the observed frequencies of i.r. absorption spectra in detail, a normal coordinate analysis has been accomplished for the complexes of the first type as a 33-body problem. Copper(II) and zinc(II) complexes with l-threonine have been prepared for comparison.