Synthesis, crystal structure and properties of the trigonal–bipyramidal complex tris(2-methylpyridine N-oxide-κO)bis(thiocyanato-κN)cobalt(II)

Abstract

Reaction of Co(NCS)2 with 2-methylpyridine N-oxide in a 1:3 ratio in n-butanol leads to the formation of crystals of tris(2-methylpyridine N-oxide-κO)bis(thiocyanato-κN)cobalt(II), [Co(NCS)2(C6H7NO)3]. The asymmetric unit of the title compound consists of one CoII cation two thiocyanate anions and three crystallographically independent 2-methylpyridine N-oxide coligands in general positions. The CoII cations are trigonal–bipyramidally coordinated by two terminal N-bonding thiocyanate anions in the trans-positions and three 2-methylpyridine N-oxide coligands into discrete complexes. These complexes are linked by intermolecular C–H...S interactions into double chains that elongate in the c-axis direction. Powder X-ray diffraction (PXRD) measurements prove that all batches are always contaminated with an additional and unknown crystalline phase. Thermogravimetry and differential analysis of crystals selected by hand reveal that the title compound decomposes at about 229°C in an exothermic reaction. At about 113°C a small endothermic signal is observed that, according to differential scanning calorimetry (DSC) measurements, is irreversible. PXRD measurements of the residue prove that a poorly crystalline and unknown phase has formed and thermomicroscopy indicates that some phase transition occurs that is accompanied with a color change of the title compound.