SYNTHESIS AND CHARACTERIZATION OF COBALT(III) AZIDO COMPLEXES OF SOME PYRIDINE LIGANDS AND X-RAY CRYSTAL-STRUCTURE OF MER-[CO(PYRIDINE)3(N3)3] AND MER-[CO(4-PICOLINE)3(N3)3]

A series of green cobalt(III) azido complexes of the type CoL3(N3)3, where L is pyridine, 4-amino-, 4-ethyl- or 3-methyl-pyridine, in addition to another series of brown complexes of the same type for L = 4-methyl-, 4-bromo-, 4-aldehyde-, 4-acetyl, 4-cyanopyridines and methyl-, ethyl-nicotinate and isonicotinates, have been prepared by aerial or persulphate oxidation of cobalt(II). The complexes gave non-conducting solutions and their electronic spectra are discussed. The IR spectral results suggest asymmetric azido ligands, whereas the number of Co-N(N3) and Co-N(L) stretching bands observed in the far-IR region are consistent with mer-formulation of complexes of both series. X-ray crystal structure determinations were done for mer-[Co(py)3(N3)3] (1) and mer-[Co(4-pic)3(N3)3] (2). The coordination around the cobalt(III) ion in the discrete molecules of both compounds is approximately octahedral with mean Co-N(L) distances of 1.977(7) and 1.973(12) angstrom and Co-N(N3) lengths of 1.951(9) and 1.949(10) angstrom for 1 and 2, respectively.