Synthesis, characterization and kinetic studies of the formation of a new chromium( III)‎ complex of mixed ligands L-cysteine and picolinic acid

Abstract EN

A new Cr (III) complex of mixed ligands of picolinic acid (Hpic) and Lcysteine has been synthesized from acid catalyzed hydrolysis of the blue colored solution of sodium salt of bis L-cysteinato (N, O, S) chromateIII complex with solution of Hpic restrictive acidic media of pH = 3-4 with gentle heating.

The red-brown color product complex of sodium bis L-cysteinato (N, O) monohydroxy picolinato (N) chromateIII have been characterized by element analysis, electronic and i.

r spectroscopy comparison to the properties of some well known related Cr (III) complexes leads to the conclusion that Hpic binds to Cr (III) center via its nitrogen donor atom.

The kinetics and mechanism of the formation of this complex, from the acid catalyzed cleavage of Cr—S bond and subsequent Hpic substitution, have been studied spectrophotometrically in a limited pH 3-4.5 range, which was adjusted by HClO4 (μ = 0.2M).

The rate of the production shows two reaction paths ; one for mono protic thiol, [ Cr (III) (L-cysH) (L-cysN, O, S) (H2O)] and other for diprotic both thiol, [Cr (L-CysH)2 (H2O)2] + 2, with Hpic ligand substitution on Cr (III) through N atom.The speices of monoprotic reacts faster with an acid dependent than the diprotic species reaction.

The pseudo first order rate constant equation is of the form ; k = k1Ka2 [H +]-1 + k2 (where k1 represents the rate constant for first step, k2 for second step reactions and Ka2 is acid dissociation constant for diprotic species) was obtained with ΔH # and ΔS # for both paths are 67.195 kJ mol-1, - 25.41JK-1mol-1 and 68.96 kJ mol-1, -93.64 JK-1 mol-1 respectively.