The metal complexes of amino acids and their N-substituted derivatives—VII. The i.r. spectra and normal coordinate analyses of bivalent metal complexes with N-methylglycine and N-phenylglycine

Abstract

Twelve complexes of bivalent metals with N-methylglycine (sarcosine) and N-phenylglycine have been prepared over wide pH ranges and characterized by means of i.r. powder diffuse reflection, electronic spectra and magnetic susceptibility. These complexes are classified into two types, either with or without chloride ions, from elemental analyses: the former type (A) consists of ML 2· nH 2O (M = Co, Ni, Cu, Zn for L = sarcosinate anion; M = Co, Ni, Cu, Zn, Cd for L = N-phenylglycinate anion), which appear to be octahedral complexes. The metal is coordinated through a nitrogen atom, a carboxyl oxygen atom and water molecules or the carboxyl oxygen atoms of neighboring molecules. The latter type (B) consists of CoCl 2 (HL) 2·2H 2O, ZnCl 2 (HL) 2 and CdCl 2 (HL) (HL = sarcosine), in which the ligand has a zwitterion structure and has metal ions coordinated through only a carboxyl oxygen atom, but does not chelate through a nitrogen atom. In the cadmium (II) complex, a chloride ion seems to bridge to two cadmium (II) ions. In order to assign the observed frequencies of i.r. spectra in detail, normal coordinate analyses have been carried out for the complexes of the A type. The frequency separation of COO − antisymmetric and symmetric vibrations of A type complexes with sarcosine increases in the order: Co (II) < Ni (II) < Zn (II) < Cu (II). These separations of A type complexes with sarcosine and N-phenylglycine are larger than those of the corresponding complexes with glycine, alanine and other α-amino acids. The frequencies of metal-nitrogen and metal-oxygen stretching vibrations increase in the order: Co (II) < Zn (II) < Ni (II) < Cu (II) for sarcosine A type complexes.