CHROMIUM(III) COMPLEXES OF NATURALLY-OCCURRING LIGANDS

Chromium(III) complexes prepared from CrCl3Py3 and anhydrous CrCl3 wit h L(-)-threonine, nicotinic acid, glycine, D(-)-penicillamine, L(-)-cy steine 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 s pectra two sharp peaks are observed at (15.9-19.8) x 10(3) and (22.0-2 6.7) x 10(3) cm-1 and are assigned to d-d transitions in the pseudo oc tahedral configuration. The parameters (D(q), B, beta35) and the inter electronic repulsion parameter with the ionic charge, Z, are calculat ed and place the ligand in the middle of the spectrochemical series. I n the circular dichroism spectra three Cotton effects are observed in the forbidden band of the optically active chelates and are assigned t o the 2E(2Eg), A2-2 (T1g-2) and E-2(Tlg-2) while that in the spin allo wed band are a result of the splitting of the A2g-4(T2g-4) to A1-4(T2g -4) and E-4(T2g-4) transitions. The structure of theonine, cystine and cysteine chelates are likely to be fac since strong and well defined Cotton effects are observed. The Cotton effects of penicillamine chela tes are weak suggesting formation of the mer structure. Prolonged heat ing or bubbling air through the solution of CrCl3Py3 containing L(-)-t hreonine, glycine or nicotinic acid for several hours enhances chromiu m(VI) formation.