Preparation and Absorption Spectra of the Cobalt(III) Complexes of Amino Acids

Three different methods were investigated of the preparation of trisglycinato-, trisalaninato- and trisleucinatocobalt(III). The method using cobalt(III) hydroxide is convenient for the α-form, the method using hexammine-cobalt(III) salt is advantageous for the β-form, and the method using tricarbonatocobaltate(III) gives both forms of the complexes. In addition, two new isomers of [Co en(ata)]·H2O and [Co(NH3)3cit]·H2O having trans-cis and cis-cis configurations with respect to the coordinated atoms were synthesized. By comparing the visible and the ultraviolet absorption spectra, it was concluded that the α-form is a trans-cis isomer and that the β-form is a cis-cis isomer. Thermal decomposition of the complexes was performed in order to estimate the water of crystallization and the stability. The infrared spectra of the complexes were also measured.