Equilibrium studies of reactions of 4-chloro-1,2-diaminobenzene, 4-methyl-1,2-diaminobenzene, 4-methoxy-1,2-diaminobenzene and 4,5-dimethyl-1,2-diaminobenzene with dinuclear cobalt(II) 1,4,7,13,16,19-hexaaza-10,22-dioxacyclotetracosane