Four new mononuclear Ni(II) complexes [Ni(L¹)]ClO₄ (1a), [Ni(L²)]ClO₄(1b), [Ni(SCN)₃(CH₃OH)(aminoethylpiperazineH)] (2a), and [Ni(DMSO)₄(aminoethylpiperazineH)](ClO₄)₃(2b)have been synthesized from two Schiff base ligands [L¹ = 1-phenyl-3-((2-(piperidin-4-yl)ethyl)imino)but-1-en-1-ol and L² = 4-((2-(piperazin-1-yl)ethyl)imino)pent-2-en-2-ol] by exploiting the flexibility of the piperazinyl moiety. Structural analysis reveals that 1a and 1b are square planar complexes with piperazine rings in boat conformations whereas hydrolysis of Schiff bases (L¹ and L²) occurs during formation of octahedral complexes (2a and 2b) with piperazine rings in chair conformations. Screening tests were conducted to quantify the binding ability of complexes (1a, 1b and 2a) towards DNA, BSA and HSA and it was found that square planar complexes (1a and 1b) showed more effective binding properties over octahedral complex (2a). Furthermore, enzyme kinetic studies reflect that square planar complexes (1a and 1b) are also effective in mimicking catecholase like activities over octahedral complex (2a). Among all the complexes, 1a was found to be the most promising molecule among the series due to its large binding affinity towards different bio-macromolecules and higher T.O.N in the catechol oxidation reaction.

Two new metal–organic compounds {[Cu₃(μ₃-4-ptz)₄(μ₂-N₃)₂(DMF)₂](DMF)₂}_n (1) and {[Cu(4-ptz)₂(H₂O)₂]}_n (2) {4-ptz = 5-(4-pyridyl)tetrazolate} with 3D and 2D coordination networks, respectively, have been synthesized while studying the effect of reaction conditions on the coordination modes of 4-pytz by employing the [2 + 3] cycloaddition as a tool for generating in situ the 5-substituted tetrazole ligands from 4-pyridinecarbonitrile and NaN₃ in the presence of a copper(II) salt. The obtained compounds have been structurally characterized and the topological analysis of 1 discloses a topologically unique trinodal 3,5,6-connected 3D network which, upon further simplification, results in a uninodal 8-connected underlying net with the bcu (body centred cubic) topology driven by the [Cu₃(μ₂-N₃)₂] cluster nodes and μ₃-4-ptz linkers. In contrast, the 2D metal–organic network in 2 has been classified as a uninodal 4-connected underlying net with the sql [Shubnikov tetragonal plane net] topology assembled from the Cu nodes and μ₂-4-ptz linkers. The catalytic investigations disclosed that 1 and 2 act as active catalyst precursors towards the microwave-assisted homogeneous oxidation of secondary alcohols (1-phenylethanol, cyclohexanol, 2-hexanol, 3-hexanol, 2-octanol and 3-octanol) with tert-butylhydroperoxide, leading to the yields of the corresponding ketones up to 86% (TOF = 430 h⁻¹) and 58% (TOF = 290 h⁻¹) in the oxidation of 1-phenylethanol and cyclohexanol, respectively, after 1 h under low power (10 W) microwave irradiation, and in the absence of any added solvent or additive.

In the last two decades, metal organic frameworks (MOFs) have been extensively investigated to develop heterogeneous electrocatalysts for water oxidation (WO). The scope of reticular synthesis, enormous surface area and accessible internal volume of MOFs make them promising candidates for catalysis. However, low electrical conductivity, slow mass transport and lack of stability restrict the scope of MOF-based WO. In recent times, various material designing approaches, e.g., the introduction of mixed metal and multi-metal systems, ligand engineering, guest@MOF composite formation, preparation of thin films, MOF composite formation with conducting carbon-based materials, metal oxides, polymers and layered compounds, etc. have emerged as an effective means to counteract the aforementioned limitations. This feature article critically discusses the common MOF-based material designing strategies with respect to electrochemical WO and provides a platform to understand the potential of MOFs to prepare a sophisticated hybrid electrocatalyst for WO.

Two new mononuclear water soluble copper(II) complexes, [Cu{(5-pyrazinyl)tetrazolate}₂(1,10-phenanthroline)] 1 and [Cu{(5-pyrazinyl)tetrazolate}(1,10-phenanthroline)₂](NO₃)_0.5(N₃)_0.52, have been synthesized using the metal mediated [2 + 3] cycloaddition reaction between copper bound azide and pyrazinecarbonitrile. The interactions of these copper tetrazolate complexes 1 and 2 with biomolecules like DNA and bovine serum albumin (BSA) are studied and the catecholase like catalytic activity of compound 2 is also explored. Structural determination reveals that both compounds 1 and 2 are octahedral in nature. Screening tests were conducted to quantify the binding ability of complexes (1 and 2) towards DNA and it was revealed that complex 2 has a stronger affinity to bind to CT-DNA. DFT studies indicated that a lower HOMO–LUMO energy gap between the DNA fragment and metal complexes might be the reason for this type of stronger interaction. DNA cleavage activity was explored by gel-electrophoresis and moderate to strong DNA cleavage properties were observed in the presence and absence of co-reagents. Inhibition of cleavage in the presence of sodium azide indicates the propagation of the activity through the production of singlet molecular oxygen. Furthermore enzyme kinetic studies reflect that complex 2 is also effective in mimicking catecholase like activities. An ESI-MS spectral study indicates the probable involvement of dimeric species [(phen)₂Cu-(OH)₂-Cu(phen)₂]²⁺ in the catalytic cycle.