Optically active co-ordination compounds. Part XVIII. Conformations of labile complexes in solution

Abstract

The circular dichroism spectra of some optically active, kinetically labile, co-ordination complexes diluted in potassium halide discs have been measured and compared with the spectra obtained in aqueous solutions. Good agreement between the two phases was found for the 1 : 2 complexes of copper(II) with the bidentate ligands L-isoleucine, L-valine, L-tyrosine, (+)-pseudoephedrine and L-proline. Except for L-proline, the configuration in both the solid state and aqueous solution for these complexes is definitely established as trans. Similarly, the cis-bistridentate nature of bis(L-histidinato)nickel(II) in aqueous solution and the dimeric nature of the (+)-tartratovanadyl(IV) ion in aqueous solution are confirmed. Dissimilar spectra between the two phases were found for the 1 : 2 complexes of copper(II) with bidentate L-alanine and L-threonine ligands and these are discussed in terms of the configuration around the copper(II) ion, and the conformation and facultative character of the ligands.