Synthesis, crystal structure and thermal behavior of tetrakis(3-cyanopyridine N-oxide-κO)bis(thiocyanato-κN)cobalt(II), which shows strong pseudosymmetry

Abstract

The title compound, [Co(SCN)2(C6H4N2O)4], was prepared by the reaction of cobalt(II)thiocyanate with 3-cyanopyridine N-oxide in ethanol. In the crystal, the cobalt(II) cations are octahedrally coordinated by two terminal N-bonded thiocyanate anions and four O-bonded 3-cyanopyridine N-oxide coligands, forming discrete complexes that are located on centers of inversion, hence forming trans-CoN2O4 octahedra. The structure refinement was performed in the monoclinic space group P21/n, for which a potential lattice translation and new symmetry elements with a fit of 100% is suggested. The structure can easily be refined in the space group I2/m, where the complexes have 2/m symmetry. However, nearly all of the reflections that violate the centering are observed with significant intensity and the refinement in P21/n leads to significantly lower R(F) values (0.027 versus 0.033). Moreover, in I2/m much larger components of the anisotropic displacement parameters are observed and therefore, the crystal structure is presented in the primitive unit cell. IR investigations confirm that the anionic ligands are only terminally bonded and that the cyano group is not involved in the metal coordination. PXRD investigations show that a pure crystalline phase has been obtained and measurements using simultaneously thermogravimetry and differential thermoanalysis reveal that the compound decomposes in an exothermic reaction upon heating, without the formation of a coligand-deficient intermediate phase.