Labile Cobalt Research Articles

Reactions of complex compounds of cobalt. Part IX. Ammonia exchange during the base hydrolysis of chloropenta-amminecobalt(III) ion in concentrated aqueous ammonia

In unsuccessful attempts to detect kinetically labile cobalt(II) species (intermediates in a postulated redox mechanism) the ammonia exchange during base hydrolysis of [Co(15NH3)5Cl]Cl2 in concentrated aqueous ammonia was examined. At ca. 23 °C there was less than 1% exchange. 15N/14N analyses were done by a novel method using 1H magnetic resonance. Experimental details are given.

Effect of Electrolytes on the Catalytic Racemization of Tris(Ethylenediamine)-Cobalt(III) Ion

ACTIVATED carbon has been used as a catalyst in a number of methods for the preparation of cobalt-(III) complexes. It has been shown that the racemization of tris(ethylenediamine)cobalt(III) ion1 and other cobalt(III) complexes2 is accelerated in the presence of activated carbon. Since the rate of exchange in the system [Co(en)3]3+−*en in the presence of charcoal is slower than the rate of racemization of d-[Co(en)3]3+, the racemization cannot be attributed solely to a ligand exchange process3. Dwyer and Sargeson4 have observed that on boiling a solution of d-tris(ethylenediamine)cobalt(III) chloride with activated carbon for 3 min., the optical activity was lost completely and about 4 per cent of the total cobalt was reduced to Co2+. In the presence of sulphuric acid (0.1 N) and carbon, the complex was reduced to about the same extent, but the optical rotation decreased only slightly (by 6 per cent). They interpreted these results to mean that the racemization occurs through an electron exchange process involving [Co(en)3]2+. Sulphuric acid would destroy the labile cobalt(II) complex and inhibit the racemization by this mechanism.