Mn(II) complexes of different nuclearity: synthesis, characterization and catecholase-like activity

The origin of catecholase-like activity of Mn(ii)–Schiff-base complexes has been explored by studying structurally characterized mono-, di- and polynuclear Mn(ii) complexes of two "end-off" compartmental Schiff-base ligands

Dinuclear copper(II) complexes: Solvent dependent catecholase activity

Four new dicopper(II) complexes of phenol based compartmental ligands, namely [Cu2(L1H)2(H2O)2(NO3)2] (NO3)2 (1), [Cu2(L2)(OH)(H2O)(NO3)](NO3) (2), [Cu2(L3)2(H2O)(NO3)](NO3) (3) and [Cu2(L4)(H2O)2(NO3)] (NO3)2 (4) [where L1 = 2-formyl-4-methyl-6-(4-(aminomethyl)-piperidine)iminomethyl-phenolato, L2 = 2,6-bis(2-amino-2-methyl-1-propanol)iminomethyl-4-methyl-phenolato, L3 = 2-formyl-4-methyl- 6-(benzylamine) iminomethyl-phenolato and L4 = 2,6-bis(2-aminoethylpyridine)iminomethyl-4-methyl-phenolato] have been synthesized and structurally characterized. The single crystal X-ray analyses reveal that all four complexes are dinuclear in nature; complexes 2 and 4 comprise of one respective ligand, whereas 1 and 3 are contain two respective ligands, and the Cu\u2013Cu separation in each case is ca. 3.0 \uc5. All four complexes are soluble in dichloromethane (DCM), methanol, acetonitrile (ACN), dimethylsulfoxide (DMSO), water\u2013methanol (50:50, v/v), and this property has been exploited to access the solvent effect on the catecholase activity of the complexes towards the aerobic oxidation of 3,5-DTBC to 3,5-DTBQ. A UV\u2013Vis spectral study in the different solvents, followed by a kinetic investigation, suggests that the change in spectral behavior follows a similar trend, being dependent on the coordinating ability of the solvent, irrespective of the complex used. The commonly known physical parameters of the solvents, like the dielectric constant, dipole moment, polarity, etc., do not seem to be a key factor in controlling the catecholase activity. However, protic solvents are observed to be a better choice than aprotic solvents for the oxidation of 3,5-DTBC

A series of mononuclear nickel(II) complexes of Schiff-base ligands having N,N,O- and N,N,N-donor sites: Syntheses, crystal structures, solid state thermal property and catecholase-like activity

Four new mononuclear nickel(II) complexes, namely [NiL1(H2O)3](NO3)2 (1), [NiL2(H2O)3](NO3)2 (2), [NiL3(H2O)3](NO3)2 (3) and [NiL4(ClBz)(H2O)] 1.25(H2O) (4) have been synthesized via Schiff-base formation by condensation between 2-benzoylpyridine and N-(2-aminoethyl)pyrrolidine for L1, salicylaldehyde and N-(2-aminoethyl)piperazine (L2), 5-chlorosalicylaldehyde and N-(2-aminoethyl)piperazine (L3), and 5-chlorosalicylaldehyde and N-(2-aminoethyl)morpholine (L4). These complexes are comprehensively characterized via routine physicochemical techniques as well as by single crystal X-ray structural analyses. Despite all the nickel complexes are mononuclear, the catecholase activity shows prominent variation depending on the coordination environment around the metal center. Complexes 2 and 3 derived from same amine bear an extra positive charge on the ligand system facilitating the substrate\u2013catalyst interaction to promote the oxidation of 3,5-DTBC to 3,5-DTBQ. On the contrary complexes 1 and 4 remain inert in nature, although 1 shows structural similarities in terms of coordination environment with nickel substituted catechol oxidase

A novel single pot synthesis of binuclear copper(II) complexes of macrocyclic and macroacyclic compartmental ligands: Structures and magnetic properties

Two binuclear copper(II) complexes one (complex 1) with a macrocyclic ligand (H(2)L1) and other (complex 2) with a macroacyclic (end-off type) compartmental ligand (HL2) have been synthesized from single pot template synthesis involving copper(II) nitrate, 1,2diaminoethane, 4-methyl-2,6-diformylphenol, and sodium azide. Structure analysis of complex I reveals that there are actually two half molecules present in the asymmetric unit and so two complexes (molecule-I and molecule-II) are present in unit cell, although they show slight differences. The two Cu(II) centers are in distorted square pyramidal coordination environment with two endogenous phenoxo bridges provided by the phenolate of H(2)L1 I having Cu-Cu separations of 2.9133(10) angstrom and 2.9103(10) in the two molecules. In complex 2 the coordination environments around two Cu(II) centers are asymmetric, Cu1 is in distorted square pyramidal environment whereas, the coordination environment around Cu2 is distorted octahedral. The two Cu(II) centers in complex 2 are connected by two different kinds of bridges, one is endogenous phenoxo bridge provided by the phenolate of the ligand HL2 and the other is exogenous azido bridge (mu-(1),(l) type) with Cu-Cu distance of 3.032(10) angstrom. Variable temperature magnetic studies show that two Cu(II) centers in both the complexes are strongly antiferromagnetically coupled with J = -625 +/- 5 cm(-1) and J = -188.6 +/- 1cm(-1) for complex 1 and 2, respectively. (C) 2006 Elsevier B.V. All rights reserved