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Shrīrāmpur, India

Mandal T.N.,University of Calcutta | Roy S.,University of Calcutta | Konar S.,University of Calcutta | Jana A.,University of Calcutta | And 9 more authors.
Dalton Transactions | Year: 2012

The ditopic ligand PyPzOAPz (N-[(Z)-amino(pyrazin-2-yl)methylidene]-5- methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazonic acid) was synthesized by in situ condensation of methyl imino pyrazine-2-carboxylate with 5-methyl-1-(2-pyridyl) pyrazole-3-carbohydrazide. In this work we have also used two of our earlier ligands PzCAP (5-methyl-N-[(1E)-1-(pyridin-2-yl)ethylidene]- 1H-pyrazole-3-carbohydrazonic acid) (Dalton Trans., 2009, 8215) and PzOAP (N-[(Z)-amino(pyridin-2-yl)methylidene]-5-methyl-1H-pyrazole-3-carbohydrazonic acid) (Dalton Trans., 2007, 1229). These ligands PzCAP, PzOAP and PyPzOAPz were made to react with Mn(ClO 4) 2.6H 2O to produce three pentanuclear Mn(ii) clusters [Mn 5(PzCAP) 6](ClO 4) 4 (1), [Mn 5(PzOAP) 6](ClO 4) 4 (2) and [Mn 5(PyPzOAPz) 6] (ClO 4) 4 (3). These complexes have been characterized by X-ray structural analyses and variable temperature magnetic susceptibility measurements. All complexes have a pentanuclear core with trigonal bipyramidal arrangement of Mn(ii) atoms, where, the axial metal centers have a N 3O 3 chromophore and the equatorial centers have N 4O 2 with an octahedral arrangement. These Mn 5(ii) clusters 1, 2 and 3 show the presence of antiferromagnetic coupling within the pentanuclear manganese(ii) core (J = -2.95, -3.19 and -3.00 cm -1 respectively). Density functional theory calculations and continuous shape measurement (CShM) studies have been performed on these complexes to provide a qualitative theoretical interpretation of the antiferromagnetic behaviour shown by them. The pentanuclear Mn(ii) cluster (1) on reaction with Cu(NO 3) 2.6H 2O in 1:1 mole proportion in CH 3OH:H 2O (60:40) forms a homoleptic [2 × 2] tetranuclear Cu 4(ii) grid [Cu 4(PzCAP) 4(NO 3) 2](NO 3) 2.8H 2O (4). The same Cu 4(ii) grid is also obtained from a direct reaction between the ditopic ligand PzCAP with Cu(NO 3) 2.6H 2O in 1:1 mole proportion. This conversion of a cluster to a grid is a novel observation. © 2012 The Royal Society of Chemistry. Source

Das M.,Jadavpur University | Chatterjee S.,Serampore College Serampore | Harms K.,University of Marburg | Mondal T.K.,Jadavpur University | Chattopadhyay S.,Jadavpur University
Dalton Transactions | Year: 2014

A dinuclear and a novel bi-cyclic hetero trinuclear bis(μ-tetrazolato) bridged nickel(ii) Schiff base complexes [Ni2(L1) 2(PTZ)2] (1) and [Ni2(L2) 2(PTZ)2Na(H2O)]ClO4·H 2O (2) {where HL1 = 2-((2-(dimethylamino)ethylimino) methyl)-6-methoxyphenol, HL2 = 2-((2-(methylamino)ethylimino)methyl)- 6-methoxyphenol and HPTZ = 5-(2-pyridyl)tetrazole} have been synthesized by in situ 1,3-dipolar cyclo-addition and characterized by spectral analysis, X-ray crystallography, and variable-temperature magnetic susceptibility measurements. Both the complexes crystallize in monoclinic space group P21/c. Both the complexes feature double μ-NN′-tetrazolato bridged dinickel(ii) structures, in which each nickel(ii) is coordinated meridionally by a depronated terdentate Schiff base [(L1)- for 1 and (L 2)- for 2] and two nitrogen atoms of the (PTZ) -. A nitrogen atom from a symmetry related bridging (PTZ)- coordinates to complete the distorted octahedral geometry of nickel(ii). The phenoxo and methoxo oxygen atoms from two [NiL2] units and a water molecule coordinate to a sodium(i) to form the unique bi-cyclic trinuclear nickel(ii)-sodium(i)-nickel(ii) core in complex 2. Very strong π⋯π stacking is observed in complex 2 to form a supramolecular chain. The variable-temperature (1.8-300 K) magnetic susceptibility measurements show the presence of anti-ferromagnetic coupling between two nickel(ii) centers for both complexes with J = -2.14(1) cm-1 (for 1) and J = -1.20(2) cm -1 (for 2). To obtain a better understanding of the magnetic exchange mechanism, quantum mechanical (DFT) calculations have been performed. The calculated J values [Jtheo = -4.53 cm-1 (for 1) and J theo = -2.48 cm-1 (for 2)] are in agreement with the values obtained experimentally. © 2014 The Royal Society of Chemistry. Source

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