Synthesis and structural characterization of two new anionic cobalt(III) azide complexes of 2,3- and 2,5-pyridine dicarboxylic acids

The oxidation of cobalt(II) ions in presence of azide ions and 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-pyridine dicarboxylic acids afforded only solid complexes in case of 2,3-pyridine dicarboxylic acid (2,3-H2L): [Co(2,3-L)(2)(N-3)(2)][Na-3(H2O)(10)] (1) and 2,5-pyridine dicarboxylic acid (2,5-H2L): [Co(2,5-L)(2)(N-3)(2)][Na-3(H2O)(8)](H2O)(2) (2). The electronic and IR spectra and thermal analysis of these two complexes are measured and discussed. X-ray single crystal analysis has shown both complexes to contain anionic mononuclear [Co(2,x-L)(2)(N-3)(2)](3-) in which the trivalent cobalt atom, located at the inversion center, is six-coordinated with trans-octahedral geometry. The CoN4O2 chromophore is formed by N and O atoms of two chelating 2,3- or 2,5-pyridine dicarboxylato anions and two N atoms of mono dentate azide ligands. In both complexes, the chelating-COO- groups in position 2 are asymmetric [Delta(C-O)=0.064(3) for 1 and Delta(C-O)=0.059(5) angstrom for 2] and coplanar to the central pyridine ring whereas the non-chelating-COO- groups have symmetric C-O bonds. The azido groups are asymmetric and linear within experimental error. Hydrogen bonds of different types connect the anions and polymeric [Na-3(H2O)(n)](3-) polyhedra giving supramolecular networks. (C) 2005 Elsevier Ltd. All rights reserved.