1,1-Dimethylbiguanide hydrochloride (metformin) is a strong base. It forms well defined salts and possessing excellent coordination capacity with transition metals, forming highly colored bidentate chelate complexes. Metformin (MET) exists in various forms: diprotonated (H2MET)2+ in strong acidic solution, monoprotonated (HMET)+ in weak acid, MET in neutral and deprotonated (MET)- in strong alkali solution.