An unprecedented solid of coper(II) complexes [Cu(dpa)₂NCS]₂[Cu(dpa)₂(NCS)₂](ClO₄)₂ (1) [dpa = 2,2'-dipyridylamine; SCN = thiocyanate], has been synthesized and crystallographically characterized with the aim to study the catecholase activity. The Cu(II) complex mimics the full catalytic cycle of the active site of catechol oxidase enzyme in acetonitrile medium with a turnover number of 4.788 × 10³ h⁻¹ along with the production of semiquinone radical and hydrogen peroxide. In situ generation of Cu(I) species in the catalytic pathway of catechol oxidation was established by electrochemical study and further confirmed by electron paramagnetic resonance (EPR) spectroscopy.

A mononuclear cobalt(II) complex, [Co(phen) ₂Cl ₂], (phen = 1,10-phenanthroline) has been synthesized and structurally characterized by different spectroscopic methods including single crystal X-ray structural study.X-ray crystal structural analysis revealed that the cobalt(II) complex crystallizes in amonoclinicsystem with C2/c space group and exists in cis-configuration in its crystalline state. Room temperature magnetic measurement accounts for 3e paramagnetism and indicates high spin cobalt(II) in the solid state. The cobalt(II) complex has been evaluated as a functional model for phosphatase enzyme by using 4-nitrophenylphosphate (PNPP) as a standard substrate in aqueous DMF medium. This mononuclear cobalt(II) complex exhibits good hydrolytic phosphoester cleavage efficiency with k_cat value of 3.78 × 10 ²h ⁻¹.

In this work, we have synthesised and structurally characterized a mononuclear cobalt(III) complex,[Co(2-O-pn)₂] Cl 2H₂O (1), (2-O-pn = 1,3-diamino-2-propanolate). From the X-ray structure of the cobalt complex, it is revealed that Co(III) ion in 1 adopts an octahedral geometry and crystallizes in the monoclinicsystem with C2/c space group. The lattice aqua molecule in combination with chloride ion in 1 forms a waterchloride cluster, (H₂O)₂ ··· (Cl)₂ through strong H-bonding interaction mediated via cobalt(III) complex in a unique binding motif. This cobalt(III) complex has been tested as an effective catalytic system towards the oxidative coupling of 2-aminophenol (2-AP) in the MeCN medium. In situ mass spectral analysis confirms that 2-AP forms an adduct with cobalt ion and the course of catalysis proceeds through catalyst-substrate binding followed by oxidative coupling of 2-AP with iminobenzoquinone. This cobalt(III) catalyst affords exclusively aminophenoxazinone species with a significant turnover number, k_cat: 6.37×10²h^-1 in the MeCN medium. This cobalt(III) complex is able to screen out the growth of some bacteria and fungi species. Quantum chemicalcalculations employing density functional theory is used to model structural parameters and spectroscopic behaviour. The theoretical findings corroborate well with the experimental results.