Chromium(III) complexes of naturally occurring ligands

Abstract

Chromium(III) complexes prepared from CrCl3Py3 and anhydrous CrCl3 with l(-)-threonine, nicotinic acid, glycine, d(-)-penicillamine, l(-)-cysteine and l(-)-cystine have been characterized. The magnetic moments (3.4-4.05 B.M.) are close to the spin only value for a d3 chromium(III) ion in octahedral or pseudo octahedral symmetry. In the electronic spectra two sharp peaks are observed at (15.9-19.8) × 103 and (22.0-26.7) × 103 cm-1 and are assigned to d-d transitions in the pseudo octahedral configuration. The parameters (Dq, B, β35) and the interelectronic repulsion parameter with the ionic charge, Z*, are calculated and place the ligand in the middle of the spectrochemical series. In the circular dichroism spectra three Cotton effects are observed in the forbidden band of the optically active chelates and are assigned to the 2E(2Eg), 2A2(2T1g) and2E(2T1g) while that in the spin allowed band are a result of the splitting of the 4A2g(4T2g) to 4A1(4T2g) and4E(4T2g) transitions. The structure of threonine, cystine and cysteine chelates are likely to be fac since strong and well defined Cotton effects are observed. The Cotton effects of penicillamine chelates are weak suggesting formation of the mer structure. Prolonged heating or bubbling air through the solution of CrCl3Py3 containing l(-)-threonine, glycine or nicotinic acid for several hours enhances chromium(VI) formation. © 1995.