Table 2. Comparison of the anticancer properties of cobalt complexes with similarly structured complexes of other first transition series metals.

S. No.	Ligands used	Complex number of the cobalt complex	Other first transition series metal used in the complex	Tested cell lines	Whether other first transition series complex is more active or less active than the cobalt complex	Ref.
1	Schiff base ligand	5	Copper	A-549 and HeLa	Copper complex was more active than complex 5	90
2	Macrocyclic ligand	49	Zinc	HeLa	Complex 49 was more active than the zinc complex	161
3	1-[Amino(thioxo)methyl]-5-hydroxy-3-methyl-1H pyrazole	63 and 64	Copper and nickel	HeLa and K562	Complexes 63 and 64 were less active than copper complexes, and had comparable activity to that of nickel complexes	199
4	Coumarin derivative	73	Manganese, nickel copper and zinc	MCF-7 and K-562	Complex 73 was many folds more active than manganese, nickel, copper and zinc complexes	221
5	Coumarinyl–pyrazolyl–thiazole thiosemicarbazone	74	Nickel and copper	HepG2	Both nickel and copper complexes were more active than complex 74	222
				MCF-7
6	Quercetin and diimine as ligands	101	Nickel and copper	A-549, PC-3, HeLa and MCF-7	Copper complexes were more active than 101, but had comparable activity to that of nickel complex	245
7	Hydrazone of 2-(2-(2,4-dihydroxybenzylidene)hydrazinecarbonyl)pyridine-1-oxide	128	Nickel, copper and zinc	MDA-MB-231 and SKOV-3	Complex 128 was less active than copper complex, however, complex 128 was much more active than nickel and zinc complexes	73
8	Thio-bis(benzimidazole)	129	Copper and zinc	CEM, MCF-7, HeLa and G-361	Complex 129 was more active than copper and zinc complexes	39
9	Sodium valproate and 1,10-phenanthroline as ligands	130	Manganese	HeLa and HepG2	Comparable activity	243