[Co(NH3)4CO3]NO3 and Na3[Co(CO3)3]·3H2O2] were synthesised as described in the literatureo Cl2·6H2O, 2-guanidinobenzimidazole (2gb), methaol, ethanol, HNO3 and Cl3CCOOH were analyticaeagents obtained from Aldrich and used withou further purification. A 1.029 N HCl Aldrich standard solution was employed.