Three copper(II) complexes, [Cu(L¹)(NCS)]_n (1), [Cu(L¹)(N₃)]_n (2) and [Cu(L²)(N₃)] (3) were synthesized from one Schiff base ligand and one reduced Schiff base ligand, (E)-4-chloro-2-[(2-propylaminoethylimino)methyl]phenol (HL¹) and 4-chloro-2-[(2-(propylaminoethylamino) methyl]phenol (HL²), respectively. All complexes were characterized by various physicochemical studies, such as FT-IR, UV-Vis, ESI-MS, EPR and single crystal X-ray diffraction. Complexes 1 and 2 have 1D polymeric chain-like structures bridging through thiocyanate and azide anions, whereas complex 3 has a mononuclear structure in the solid state. All the complexes are active towards mimicking two well-known proteins, phosphatase and phenoxazinone synthase, using the disodium salt of 4-nitrophenylphosphate (4-NPP) and 2-aminophenol (OAP) as the substrate in DMF medium. Complexes 2 and 3 show the highest activity towards phosphatase and phenoxazinone synthase activity with k_cat values of 22.6 s⁻¹ and 134.4 h⁻¹, respectively. EPR studies confirmed that for complex 1, the OAP oxidation goes through the generation of an organic radical at g = 1.99, which is due to an imine radical formation, whereas the metal center redox pathway is followed for complex 3. Extensive DFT calculations have been performed for both catalytic studies to put forward the most probable mechanistic pathways.

Four coordination compounds of formulae [Cu^II ₂(H₂L¹)(HL¹)](ClO₄)₃·H₂O (1), [Cu^II ₂(H₂L²)(CH₃OH)₂](ClO₄)₂·2CH₃OH (2), [Co^II ₂(H₂L¹)₂](ClO₄)₄ (3) and [Co^II ₂(H₂L²)₂]·2H₂O (4) were synthesized via self-assembly of succinohydrazone derived ligands (H₂L¹ = N′,N′-4-bis(2-pyridyl)succinohydrazide, H₄L² = N′,N′-4-bis(2-hydroxybenzylidene)succinohydrazide) and Cu²⁺ and Co²⁺ ions, respectively. The compounds were characterized by crystal structure determination, magnetic measurements and biological activities. Compounds 1, 3 and 4 have discrete double helicate structures, whereas compound 2 is a one-dimensional chain. Magnetic studies show antiferromagnetic exchange interactions in 2 with a J value of −67.1 cm⁻¹ and antiferromagnetic spin-canting in compound 3 originates through supramolecular H-bonding. For compound 3, a clear bifurcation was observed in zero field cooled (ZFC) and field cooled (FC) measurement at a temperature of 3.5 K and field of 0.1 T, implying long range magnetic ordering below this temperature. Interestingly, all of compounds 1–4 show significant changes in their absorption (hypo- and hyperchromism) in the presence of SS-DNA, inferring interaction between the compounds and DNA. In addition, compounds 1–4 significantly exhibited nuclease activities on both RNA and pUC19 plasmid DNA. Moreover, the nuclease activity was further enhanced in the presence of oxidant (H₂O₂) and suggests the possible role of reactive oxygen species in DNA nicking ability of compounds 1–4. Furthermore, compounds 1, 2 and 4 exhibited significant cytotoxicity against mammalian cancer cell lines (HeLa, A549 and MDAMB-231). In addition, our results from Annexin/PI staining and DNA fragmentation assays revealed that these compounds are capable of inducing apoptosis and have potential to act as anticancer drugs.