Synthesis, structural, magnetic, DFT calculations and CShM studies of three new pentanuclear Mn(ii) clusters

摘要

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.