A trinuclear zinc(II) complex [Zn₃L₂(𝜇-O₂CCH₃)₂(H₂O)₂]·H2O·2CH₃OH (1) was synthesized from an in situ reaction between zinc acetate and a Schiff base ligand (H₂L = 2-((2-hydroxyphenylimino) methyl)-6-methoxyphenol). The ligand was prepared by (1:1) condensation of ortho-vanillin and ortho-aminophenol. The ligand and zinc(II) complex were characterized by elemental analysis, Fourier Transform Infrared (FTIR), ¹H-Nuclear Magnetic Resonance (NMR), UV-Vis spectroscopy, Powder X-ray Diffraction (PXRD) and thermogravimetric analysis. 1 crystallizes in P-1 space group with 𝑎 = 11.9241(3) Å, 𝑏 = 12.19746 Å, 𝑐 = 20.47784 Å with unit cell volume is 2674.440 (Å)³. Binding property of the complex with calf thymus DNA (CT-DNA) has been investigated using absorption and emission studies. Thermal melting and viscosity experiments were further performed to determine the mode of binding of 1 with CT-DNA. Spectroscopic and viscosity investigations revealed an intercalative binding mode of 1 with CT-DNA. The ligand and its zinc complex were screened for their biological activity against bacterial species and fungi. Activity data show that the metal complex has more antibacterial and antifungal activity than the parent Schiff base ligand and against those bacterial or fungi species.

We have synthesized two isostructural mononuclear cobalt(III) complexes [1]NO₃·3H₂O and [1]NO₃·CH₃CO₂H·H₂O {[1]₊ = [Co(1,10-phenanthroline)₂Cl₂]⁺} and characterized by single crystal X-ray structural analyses. Mass spectral studies of the complexes indicate both the compounds to produce identical cationic species viz., [Co(phen)₂Cl₂]⁺ in methanol solution. [1]⁺ has been evaluated as model system for the catechol oxidase enzyme by using 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate in methanol medium, which revealed that the cationic complex efficiently inhibits catalytic activity with k_cat value 9.65 × 10² h⁻¹. [1]⁺ cleaved pBR 322 DNA without addition of an activating agent. Further, the anti-cancer activity of [1]⁺ on human hepatocarcinoma cell line (HepG2) has been examined. The induction of apoptosis induced in the cell line was assessed base on the changes in cell morphology, which showed the efficacy of [1]⁺ to induce apoptosis in 53% of cells during 24 h treatment. Interestingly, the observed IC₅₀ values reveal that [1]⁺ brings about conformational change on DNA strongly and exhibits remarkable cytotoxicity.

In this work, we have synthesised and crystallographically characterized a mononuclear iron(II) complex, [Fe(phen)₃](NO₃)₂ ·2H₂O (1) (phen = 1,10-phenanthroline). Single crystal X-ray diffraction (SXRD) analysis revealed that 1 crystallizes in monoclinic system with P 1⁻ space group. The lattice water molecules in 1 form a water-nitrate cluster, (H₂O)₂... (NO₃)₂ through strong H-bonding interaction mediated via iron(II) complex in a unique binding motif and provide additional stability to the compound in the solid state. This iron(II)complex is able to catalyze the cleavage of aromatic C-C linkage of 2,5-dihydroxybenzoic acid (Gentisic acid, GA) in oxygen environment. The iron(II) complex in the presence of two equivalent of triethylamine (Et₃N) binds with GA stoichiometrically in acetonitrile medium at 25^◦ C. Observation of GA-to-iron LMCT optical bands at 521 and 609 nm supports in situ generated iron-GA adduct in solution. This in situ generated iron-GA adduct reacts with molecular oxygen at the rate, k_obs = 6.58×10⁻³ min⁻¹ in acetonitrile and affords exclusively 2-oxo-4-hydroxy-hepta-3,5-dienedioic acid. The incorporation of both the oxygen atoms of molecular oxygen in the bio-mimicking activity of gentisate-1,2-dioxygenase by this iron(II)-phenanthroline complex remain arare example in scientific literature.