Synthesis, crystal structure and thermal properties of a new polymorphic modification of diiso-thio-cyanato-tetra-kis-(4-methyl-pyridine)cobalt(II).

The title compound, [Co(NCS)(CHN)] or Co(NCS)(4-methyl-pyridine), was prepared by the reaction of Co(NCS) with 4-methyl-pyridine in water and is isotypic to one of the polymorphs of Ni(NCS)(4-methyl-pyridine) [Kerr & Williams (1977 ▸). B, 3589-3592 and Soldatov (2004 ▸). , 1185-1194]. Comparison of the experimental X-ray powder pattern with that calculated from the single-crystal data proves that a pure phase has been obtained. The asymmetric unit consists of one Co cation, two crystallographically independent thio-cyanate anions and four independent 4-meth-yl-pyridine ligands, all located in general positions. The Co cations are sixfold coordinated to two terminally N-bonded thio-cyanate anions and four 4-methyl-pyridine coligands within slightly distorted octa-hedra. Between the complexes, a number of weak C-H⋯N and C-H⋯S contacts are found. This structure represent a polymorphic modification of Co(NCS)(4-methyl-pyridine) already reported in the CCD [Harris (2003 ▸). , 211890]. In contrast to this form, the crystal structure of the new polymorph shows a denser packing, indicating that it is thermodynamically stable at least at low temperatures. Thermogravimetric and differential thermoanalysis reveal that the title compound starts to decomposes at about 100°C and that the coligands are removed in separate steps without any sign of a polymorphic transition before decomposition.