Infrared Absorption Spectra and Normal Coordinate Analysis of Metal-Dl-α-Serine Chelates

Abstract The infrared absorption spectra of Dl-α-serine and four metal-Dl-α-serine chelates have been investigated from 4000 to 200 cm−1. A normal coordinate analysis has been accomplished for the metal chelates as a 27-body problem and an approximate description of the vibrational mode has been assigned to the observed frequencies. The frequency separation between carboxylate antisymmetric and symmetric stretching vibrations and values of the bond-stretching force constants for the metal-nitrogen bonds have been found to decrease in the order Pt(II)>Pd(II)>Cu(II)>Ni(II). These facts show that the hydroxy group in the β-position of Dl-α-serine has no influence on the order of metal-ligand bond strength, which order has been already found in aliphatic α-amino acids chelates having no hydroxy group in the β-position. Two species of copper chelates have been prepared. Though the infrared spectrum of one of them is similar to that of the nickel(II) chelate, that of the other species is different. This fact may be explained by assuming that the copper ion has been coordinated with the hydroxy group in the latter.