Dependence of the co-ordination sphere in bis(valinato)-copper(II) complexes on solvent and alkylation at nitrogen

Abstract

The ¹⁴N superhyperfine structure in the ESR spectra of bis(amino acidato)copper(II) complexes (valine, alanine and their N,N-diethylated counterparts) was studied as a function of the solvent composition and temperature. The equilibrium between two components, presumably the cis and trans isomers, was found to depend on the solvent dioxane: D₂O ratio and on temperature, in different ways for the valine and alanine complexes. Thus addition of dioxane to water solvent, and an increase in temperature from 293 K, stabilizes the valine complexes and destabilizes the alaninate complexes. This suggests a ligand–ligand interaction between the two isopropyl residues of the valinate.