The different-ligand complexes of cobalt with aromatic diamines: 2,2'-dipyridil, 1,10-phenantroline, 4,7-diphenylphenantroline and chromogen organic reagent − 2,4-dinitroben­zeneazopyrocatechol have been investigated by spectrophotometric method. The conditions of complex formation and extraction, their compositions, physic-chemical, optical and analytical properties have been determined. The extraction-photometric methods of determination of cobalt have been developed and applied for determining content of cobalt in the real objects.