3D supramolecular architectures of copper(II) complexes with 6-methylpicolinic and 6-bromopicolinic acid: Synthesis, spectroscopic, thermal and magnetic properties

Copper(II) complexes of 6-methylpicolinic (6-MepicH) and 6-bromopicolinic acid (6-BrpicH) namely, [Cu(6-Mepic)(2)(H2O)] (1), [Cu(6-MePiC)(2)(py)] (2) and [Cu(6-Brpic)(2)(H2O)] (3) were prepared and characterized by spectroscopic methods (IR, EPR). Their molecular and crystal structures were determined by X-ray crystal structure analysis, their thermal stability by TGA/DTA methods, while their magnetic properties were elucidated by the measurement of the magnetic susceptibility. X-ray structural analysis revealed an intermediate between square-pyramidal and trigonal-bipyramidal coordination polyhedron in 1 and 3 and a trigonal-bipyramidal one in 2 with the same N,C-chelated coordination mode for both 6-MepicH and 6-BrpicH in 1-3. EPR spectra showed three different types of copper(II) S = 1/2 symmetry signals. Most probably they could be assigned to the elongated axial in 1, the isotropic in 2 and the rhombic in 3. Both 1 and 2 showed the paramagnetic behaviour while 3 exhibited an anti, ferromagnetic interaction, ascribed to the formation of pseuclobinuclear units by the pi center dot center dot center dot pi stacking between pyridine rings. (C) 2008 Elsevier Ltd. All rights reserved.