Experimental and theoretical substantiation of differences of geometric isomers of copper(II) α-amino acid chelates in ATR-FTIR spectra

Stereo and structural isomerism of the copper(II) chelate complexes define their biological activity. At the same time, the identification of the geometric isomers of such complexes is a nontrivial task of modern coordination chemistry. In the presented work we have studied the trans- and cis-isomers of chelates bis(S-valinato)copper(II), (R,S-valinato)copper(II) and other mixed ligand copper(II) amino acid complexes with the joint use of experimental by ATR-FTIR spectroscopy and DFT simulations. Using DFT simulations (method M06/6 311+G(d)) the optimum conformers of the geometric isomers of copper(II) a-amino acid chelate complexes were found and their characteristic stretching vibrations were established in the mid-wave region of the IR spectra. The experimental ATR-FTIR bands of the compounds well agree with the theoretical estimates. Such a joint use allows to determine of cis- and trans-isomers of copper(II) N,O-amino acid chelates in the mid-wave region of the ATR-FTIR spectrum.