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In pursuit of the significant contribution of copper ion in different biological processes, this research work describes the synthesis, X‐ray structure, Hirshfeld surface analysis, oxidative dimerization of 2‐aminophenol and antibacterial activity of a newly designed copper (II)‐Schiff base complex, [Cu(L)2] (1), [Schiff base (HL) = 2‐(2‐methoxybenzylideneamino)phenol]. X‐ray structural analysis of 1 reveals that the Cu (II) complex crystallizes in a cubic crystal system with Ia‐3d space group. The Cu (II) centre adopts an unprecedented tetragonal bipyramidal geometry in its crystalline phase. The Schiff base behaves as a tridentate chelator and forms an innermetallic chelate of first order with Cu (II) ion. The copper (II) complex has been tested in the bio‐mimics of phenaxozinone synthase activity in acetonitrile and exhibits good catalytic activity as evident from high turnover number, 536.4 h−1. Electrochemical analysis exhibits the appearance of two additional peaks at −0.15 and 0.46 V for Cu (II) complex in presence of 2‐AP and suggests the development of AP−/AP•− and AP•−/IQ redox couples in solution, respectively. The presence of iminobenzosemiquinone radical at g = 2.057 in the reaction mixture was confirmed by electron paramagnetic resonance and may be considered the driving force for the oxidative dimerisation of 2‐AP. The existence of a peak at m/z 624.81 for Cu (II) complex in presence of 2‐AP in electrospray ionization mass spectrum ensures that the catalytic oxidation proceeds through enzyme‐substrate adduct formation. The copper (II) complex exhibits potential antibacterial properties against few pathogenic bacterial species like Staphylococcus aureus, Enterococcus and Klebsiella pneumonia and scanning electron microscope studies consolidates that destruction of bacterial cell membrane accounts on the development of antibacterial activity. [ABSTRACT FROM AUTHOR]

Abstract: In this present work, we report the synthesis and structural characterization of two copper(II) complexes, [Cu(bpy)Cl2] (1) & [Cu(μ‐Cl)(phen)Cl]2 (2) [bpy=2,2′‐bipyridine; phen=1,10‐phenanthroline]. We have also studied their catalytic fate towards phenoxazinone synthase and catechol dioxygenase activity. X‐ray structural analyses revealed that 1 & 2 crystallize in triclinic & monoclinic system with P 1 and Cc space group respectively. The copper complexes catalyse the oxidative coupling of 2‐amino phenol (2‐AP) to aminophenoxazin‐3‐one with significant turn over number, kcat(h−1)=2.08×103 & 2.16×103 for 1 & 2 resectively. During investigation of catechol dioxygenase activity, stoichiometric addition of 1 & 2 to 3,5‐di‐tert‐butylcatechol (DTBC) in acetonitrile produce in situ catecholate‐to‐Cu(II) absorption bands at 812 and 821 nm respectively. The in situ Cu(II)‐catecholate species for both 1 & 2 react with molecular oxygen at the rate, kobs: 7.95×10−4 and 1.30×10−3 min−1 respectively and produce intradiol cleavage products in exclusive amount. Minor amount of benzoquinone is also found in solution. Intradiol products are found as major product in solution and accounts in favour of substrate activation mechanism. [ABSTRACT FROM AUTHOR]

A mononuclear iron(II) complex, [Fe(phen)3]Cl2 ( 1) (phen =1,10-phenanthroline), has been synthesized in crystalline phase and characterized using various spectroscopic techniques including single crystal X-ray diffraction. Crystal structure analysis revealed that 1 crystallizes in a monoclinic system with C2/m space group. Complex 1 acts as a functional model for a biomimetic catalyst promoting the aerobic oxidation of 3,5-di- tert-butylcatechol (3,5-DTBC) through radical pathways with a significant turnover number ( kcat =3.55 × 103 h−1) and exhibits catechol dioxygenase activity towards the same 3,5-DTBC substrate at room temperature in oxygen-saturated ethanol medium. The existence of an isobestic point at 610 nm from spectrophotometric data indicates the presence of Fe3+ −3,5-DTBC adduct favouring an enzyme-substrate binding phenomenon. Upon stoichiometric addition of 3,5-DTBC pretreated with two equivalents of triethylamine to the iron complex, two catecholate-to-iron(III) ligand-to-metal bands (575 and 721 nm) are observed and the in situ generated catecholate reacts with dioxygen ( kobs =9.89 × 10−4 min−1) in ethanol medium to afford exclusively intradiol cleavage products along with a small amount of benzoquinone, and a small amount of extradiol cleavage products, which provide substantial evidence for a mechanism. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Graphical abstract This paper reports a novel addition of a Schiff base as chemosensor for nickel(II) ion in a wider range of concentration. Highlights • We developed a new chemosensor for Nickel(II) ion with high selectivity & sensitivity. • Spin state switching of nickel ion by the Schiff base remains the driving force for super stable compound. • Ratiometric fluorescence changes are observed during sensing. • This sensing technique may be applied in a wider concentration range for Ni(II) ion. • This is a pH independent sensor. Abstract A novel tetradentate (N,O)-donor salen type Schiff base was designed, prepared and structurally characterized by different analytical techniques. This Schiff base ligand, (L = 2 , 2 '-((1,2 phenylenebis(methanylylidene))bis(azanylylidene))diphenol) behaved as an effective chemosensor towards Ni(II) ion with specific selectivity. The Schiff base (L) displayed a remarkable ratiometric fluorescence enhancement upon binding with Ni(II) ion in acetonitrile (ACN) medium. The L -Ni(II) solution was distinguished indisputably with the naked eye colour change and the crystal was found to be red colour. L selectively detected Ni(II) ion in presence of other competitive cations like Mn(II), Fe(II),Co(II), Cu(II), Zn(II), Cd(II) and Hg(II) ions. This simple but novel Schiff base might be used as a potential pH independent colorimetric and naked-eye chemosensor for Ni(II) ion. Most significantly, L exhibited geometry preferred selectivity towards Ni(II) ion and formed highly stable square planar Ni(II)-Schiff base complex. Single crystal X-ray diffraction study further authenticated that the nickel complex crystallized in orthorhombic system with P 2 1 2 1 2 1 space group in solid state. Density functional theory (DFT) calculations attested the experimental results very well. This sensing method could be applied in a wider concentration range and might be used as an alternative qualitative and quantitative test for the detection of Ni(II) ion in analytical chemistry. [ABSTRACT FROM AUTHOR]

Graphical abstract Herein, the synthesis, structural characterisation and potential catalytic activity of a tetrazinc(II) complex were investigated with experimental techniques and DFT calculations. The diverse coordination aspect of methanol in the architect of the complex and it's crucial role in oxidative coupling of 2-aminophenol through ligand centred radical pathway were comprehensively ascertained. Abstract Herein, the synthesis, structural characterization and catalytic activity of a novel tetranuclear zinc(II)–Schiff base complex, [Zn 4 (L) 2 (µ 3 -OCH 3) 2 (CH 3 OH) 2 ]·2CH 3 OH (1), [ L = N,N′- bis(3-methoxysalicylidene)-1,3-diamino-2-propanol] was presented. Single crystal X-ray diffraction structural analysis revealed that the tetra-zinc(II) cluster crystallized in a monoclinic system with P 2 1 / c space group. Interestingly, three different molecular bridges (methoxido-, alkoxido- and phenoxido-) simultaneously co-existed in assembling tetra-zinc(II) core, which was a very rare observation. To the best of our knowledge, this compound would be the first compound where a diverse coordination aspect was covered by a single solvent as terminal coordinator (CH 3 OH), bridging (µ 3 -CH 3 OH) and solvent for crystallization in the existing scientific literature. The compound showed good photo-stability and excellent luminescence property with higher lifetime at transition state in ethanol. This zinc(II) complex revealed crucial role as an effective catalytic system towards oxidation of 2-aminophenol (2-AP) in ethanol. Additionally, the tetra-zinc(II) complex displayed potential phenoxazinone synthase like activity with momentous turn over number, k cat (h−1) = 6.19 × 102 in ethanol under aerobic condition. ESI-MS and EPR spectral analysis of the reaction mixture between Zn(II) complex and 2-AP recommended that the course of catalysis proceeded through substrate–catalyst adduct formation and authenticated the radical mechanistic pathway in favor of oxidative coupling product. This tetranuclear zinc(II)–Schiff base complex would be considered as the first example that catalyzed the oxidative coupling of 2-aminophenol to aminophenoxazino compound under usual aerobic condition. As complementary, detailed quantum chemical computations, performed with density functional theory (DFT) were well corroborated with the experimental results. This was the first and rarest example where a tetrazinc(II)–Schiff base cluster exhibited catalytic oxidation of 2-AP through ligand centered radical activity. [ABSTRACT FROM AUTHOR]

In this work, we have developed a new one-dimensional cadmium(II) coordination polymer, [Cd(phen)(NO 3 ) 2 (H 2 O)] n ( 1 ) (phen = 1,10-phenanthroline) and structurally characterized by different spectroscopic techniques including single crystal X-ray diffraction analysis. Single crystal X-ray structural analysis of 1 indicates that Cd(II) ion in the coordination polymer crystallizes in a monoclinic system with P 2 1 space group and adopts a distorted pentagonal bipyramidal coordination geometry. This will be the first citation of a 1D Cd(II) polymer till date where nitrate ions exhibit diverse coordination motifs. Solid state emission suggests good luminescence behavior of the polymer. Spectroscopic studies reveal that the polymer is unstable in polar solvents and dominates in monomeric form. Molar conductivity and electrospray ionization mass spectral analysis in methanolic solution confirm the instability of the polymer at room temperature and authenticates the decomposition of the polymer into monomer in solution. In addition, all the structural parameters and spectroscopic behaviors have been well corroborated with the theoretical findings. [ABSTRACT FROM AUTHOR]

An X-ray structurally characterized vanadium(V) complex, [VO 2 (L–H)] [L–H = H 2 L derived ligand (H 2 L = N,N′-(salicyaldimine)-1,3-diaminopropan-2-ol], was found to behave as an effective catalyst towards the oxidation of 3,5-di-tert-butylcatechol in methanol to its corresponding quinone derivative in aerial oxygen. The reaction follows Michaelis–Menten enzymatic reaction kinetics with a turnover number ( K cat ) of 2.063 × 10 3 h −1 . [ABSTRACT FROM AUTHOR]

An undecairon(III) oxo-hydroxo-carboxylato bridged aggregate [Fe 11 (μ 3 -O) 6 (μ 3 -OH) 6 (μ-O 2 C-f) 15 ] ( 1 ) has been synthesized and characterized by single crystal X-ray diffraction study. The anionic ligand N -(2-hydroxyethyl)-3-methoxysalicylaldimine (L) has been used as template to synthesize such high nuclearity complex. Interestingly, the ligand neither enters into the coordination sphere nor crystallizes with the iron cluster. Bond distance data indicate that all the iron atoms in 1 are high-spin Fe(III) in O-donor environment. 1 behaves as an effective catalyst towards oxidation of 3,5-di- tert -butylcatechol in different solvents, viz. methanol, dichloromethane and acetonitrile, to its corresponding quinone derivative in aerial oxygen. The reaction follows Michaelis–Menten enzymatic reaction kinetics with turnover numbers (K cat ) 3.21 × 10 3 , 1.23 × 10 3 and 1.11 × 10 3 h −1 in methanol, dichloromethane and acetonitrile, respectively. [ABSTRACT FROM AUTHOR]

A perfectly linear trinuclear zinc(II) complex [Zn3L2(µ-O2CCH3)2] (1) containing a (N,O)-donor Schiff base ligand, (H2L = N,N'-bis(salicyaldehydene)-1,3-diaminopropan-2-ol) has been synthesized and characterized by single crystal X-ray diffraction study. The X-ray crystal structure of 1 contains three zinc(II) centers which are inter-connected through µ2-phenolato and µ-acetato bridges. The terminal zinc centers are in square pyramid geometry and central zinc ion is in distorted octahedral coordination geometry. Both H2L and 1 exhibit good fluorescence properties in solution. 1 has been used as a precursor to fabricate zinc oxide nanoparticles (ZnONPs) by pyrolytic method. ZnONP has been characterized by powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), FT-IR spectroscopy and UV-Vis spectroscopy techniques. ZnONP has been employed as photocatalytic agent to degrade the organic dye, viz. Methylene blue under visible light and by exposing to visible light for 1 h, ZnONP degraded methylene blue dye nearly 80%. [ABSTRACT FROM AUTHOR]

• Synthesis and characterization of a copper(II) complex. • Solvent induced distortion to the coordination environment of Cu(II) centre. • Bio-mimics of catecholase activity with high turnover number, 4.75 × 102 h–1. • Exploitation of fungicidal and anti-proliferative property. This research work reports the synthesis, single crystal X-ray structure, catechol oxidation, fungicidal and antiproliferative activity of a newly synthesized copper(II) complex, [Cu(L) 2 ]H 2 O . CH 3 OH (1) containing an azo-functionalized Schiff base, H L = 2-methoxy-6-((Z)-((4-((E)-phenyldiazenyl)phenyl)imino)methyl)phenol. The crystal structure analysis reveals that the Cu(II) centre exists in a highly distorted square planar geometry. The crystallize water and methanol form a strong intermolecular association through H-bonding. More importantly, the H atoms of the lattice water interact with the O atoms of ligand units leading to 5- and 6-membered cycles through the H-bonding network and distort the square planar geometry. The copper(II) complex has emerged as a bioinspired catalyst in the oxidative transformation of 3,5-di- tert -butylcatechol (DTBC) to o-benzoquinone in methanol with a high turnover number, 4.75 × 102 h–1. Electrochemical analysis of the copper(II) complex in presence of DTBC recommends the generation of catechol/o-benzosemiquinone redox couple in the course of oxidation. The EPR spectral analysis of 1 in presence of DTBC was found silent and suggested the antiferromagnetic interaction between copper centre and benzosemiquinone species. The copper(II) complex turns out to be a potential fungicidal agent against clinical candida albicans and scanning electron microscope studies confirm the destruction of the fungal cell membrane with the deposition of copper. The IC 50 value of the copper complex was determined as 15 µg/mL which suggests the excellent antiproliferative potency of the synthetic compound against the breast cancer cell lines, MCF-7. [Display omitted] [ABSTRACT FROM AUTHOR]

Two hydrazine functionalized Schiff bases have been synthesized through the reaction between hydrazine and o -vanillin/salicylaldehyde compounds employing a green-chemical approach and characterized spectroscopically including XRD study. Crystal structure analysis reveals that both the chemosensors, N,N′ -bis(o -vanilidine)hydrazine (P17) and N,N′ -bis(salicylidene)hydrazine, (HARB) crystallize in monoclinic system with P 2 1 / n space group and exist in the locked forms through intramolecular H-bonding (~1.90 Å) between phenolic-OH and N atom of hydrazine. The chemosensors display excellent selectivity towards fluoride followed by bisulphate ions, over other potential competitor anions in acetonitrile. Binding stoichiometry of the individual chemosensor with F− is confirmed to be 1:1 and assessed with absorption study and 1H NMR analysis. Systematic DFT analysis reveals that the contribution of hydroxyl oxygen atoms to the HOMO increases sharply from the chemosensor to chemosensor–F− adduct (17% to 28%) leading to deprotonation of one hydroxyl group and consequently involvement in conjugation impeding the C=N isomerisation. Thus, the hydroxyl proton captured by F− restricts the C=N isomerisation as well as ICT character of both the chemosensors and confirms the cascade sensing mechanism for fluoride and bisulphate ions. This paper reports the green-chemical synthesis of hydrazine functionalized Schiff base, their crystal structures and cascade detection of fluoride followed by bisulphate ions over other competitive anions in acetonitrile in a wider range of concentration. Unlabelled Image • We developed hydrazine functionalised chemosensors for cascade detection of F− and HSO 4 − ion with high selectivity & sensitivity. • The hydroxyl proton captured by F− restricts the C=N isomerisation for the chemosensors. • DFT calculations suggests that the contribution of hydroxyl oxygen atoms to HOMO leads to deprotonation of hydroxyl group. • This sensing technique may be applied in a wider concentration range. • This is a pH independent sensor. [ABSTRACT FROM AUTHOR]

This research work demonstrates the synthesis, crystal structure, supramolecular architecture, 4-methylcatechol oxidation and bactericidal activity of a newly designed zinc complex containing a protonated Schiff base of zwitter ion type. • Synthesis and crystal structure of a tetrahedral zinc-Schiff base complex. • Schiff base gets protonated to exhibit monodentate behaviour. • The zinc complex exhibits good efficiency towards the bio-mimetic oxidation of 4-methylcatechol. • Radical driven catalytic activity has been observed. • Shows good bactericidal activity with 1.44% presence of zinc in cell membrane of bacteria. Focusing on the important biological functions of metallo-enzymes and metallo-therapeutics in living world, this research work demonstrates the synthesis, crystal structure, supramolecular architecture, 4-methylcatechol oxidation and bactericidal activity of an interesting zinc-Schiff base complex, [Zn(H L) 2 Cl 2 ] (1), [Schiff base (H L) = 2-(2-methoxybenzylideneamino)phenol]. Crystal structure analysis of the zinc-Schiff base reveals that zinc centre exists in a distorted tetrahedral geometry. The Schiff base adopts three donor centres, however it gets protonated to exist in a zwitter ionic form and behaves as a monodentate coordinator in 1. This zinc-Schiff base complex has been examined towards the bio-mimetic oxidation of 4-methylcatechol (4-MC) in methanol and portrays its good efficacy with good turnover number, 1.45 × 103 h−1. Electro-chemical study, electron paramagnetic resonance analysis and electrospray ionization mass spectrometry results for the zinc-Schiff base complex in presence of 4-MC ensures that the catalytic reaction undergoes through enzyme-substrate binding, and generation of radical in the course of catalysis drives the catalytic oxidation of 4-MC. Antibacterial study has also been performed against few clinical pathogens (Bacillus SP, Enterococcus , and E. coli). Scanning electron microscope and EDAX analysis for the pathogen with little dose of zinc complex confirms the destruction of bacterial cell membrane with 1.44% occurrence of zinc in the selected zone of inhibition area. This observation holds a great promise to develop future antibacterial agent. [ABSTRACT FROM AUTHOR]

Synthesis and structural characterization of a linkage isomer, bis(2,2′-dipyridylamine)dithiocyanato(k -S)nickel(II), [Ni(dpa) 2 (k -SCN) 2 (1) of a previously reported Ni(II) complex, [Ni(dpa) 2 (k -NCS) 2 (dpa = 2,2′-dipyridylamine; SCN = thiocyanate) has been reported herein. X-ray structural analysis of 1 reveals that Ni(II) complex crystallizes in monoclinic system with P 2 1 / c space group and exists in trans configuration. The coordination geometry for 1 adopts a tetragonal structure. Supramolecular aspects of the Ni(II) complex indicate that N atom of SCN behaves as a donor and H atom of dpa ligand acts as a receptor in growing 1D crystalline structure along b axis in solid state. The aromatic rings in 1 prefer to exist in face-centred stacking with interplanar distance of 3.426 Å and supports strongly to form self-assembled 3D crystalline architecture. Hirshfeld surface analysis further recommends this crystalline assembly in solid state. 1 exhibits promising phosphatase activity towards disodium(4-nitrophenyl)phosphate (PNPP) in aqueous-methanolic medium. The hydrolytic phosphatase efficiency for 1 is determined in terms of turnover number (k cat) as 3.38 × 104 h−1. Moreover, density functional theoretical computations closely replicate the structural parameters and spectroscopic behaviour of 1. Image 1 • Synthesis and X-ray structure of a linkage isomer, bis(2,2′-dipyridylamine)dithiocyanato(k-S)nickel(II), [Ni(dpa)2(k-SCN)2]. • The nickel(II) complex efficiently cleave PNPP with TON, 3.38 × 104 h−1. • The theoretical findings employing DFT have been well corroborated with the experimental results. [ABSTRACT FROM AUTHOR]

This paper highlights the catalytic aspects of a tetra-iron(III) cluster, [Fe 4 III(µ- O) 2 (µ- OAc) 6 (phen) 2 (H 2 O) 2 ](NO 3) 2 ·(H 2 O) 3 [phen = 1,10-phenanthroline], towards catechol oxidation and phosphoesterase activity, showing significant catalytic efficacy. An oxido- and acetato-bridged tetranuclear iron(III) cluster, [Fe 4 III(µ- O) 2 (µ- OAc) 6 (phen) 2 (H 2 O) 2 ](NO 3) 2 ·(H 2 O) 3 (1), [OAc = acetate; phen = 1,10-phenanthroline] has been prepared in the crystalline phase. X-ray structural analysis of the compound reveals that all the Fe(III) centres in 1 adopt an octahedral coordination geometry and the tetra-iron(III) core exists in an unusual asymmetric conformation. Bond valence sum (BVS) calculations recommend the existence of all iron ions in the +3 oxidation state in the crystalline phase. The tetra-iron(III) cluster elegantly catalyzes the oxidation of 3,5-di- tert -butylcatechol (DTBC), viz. catecholase-like activity, with a good turnover number, k cat = 9.28 × 102 h−1 in acetonitrile medium. Spectrophotometric titration shows the existence of two distinct isosbestic points, which unanimously proves the rarely observed enzyme-substrate binding phenomenon in solution. Electrochemical analysis recommends the production of Fe(II)–semiquinone species in the course of the catalytic oxidation of DTBC. Furthermore, the same iron(III) cluster displays phosphoester cleavage activity towards the disodium salt of p-nitrophenylphosphate (PNPP) in aqueous-methanol medium with rate of 7.20 × 10−4 m−1. ESI-MS measurements of the tetra-iron(III) complex in the presence of PNPP indicate the formation of an organophosphorus intermediate in solution and solvent aqua molecules probably make a nucleophilic attack on the phosphorus centre, favouring the generation of the organophosphorus intermediate. [ABSTRACT FROM AUTHOR]