Syntheses and crystal structures of the five- and sixfold coordinated complexes diisoselenocyanatotris(2-methylpyridine N-oxide)cobalt(II) and diisoselenocyanatotetrakis(2-methylpyridine N-oxide)cobalt(II)

The reaction of CoBr2, KNCSe and 2-methylpyridine N-oxide (C6H7NO) in ethanol leads to the formation of crystals of [Co(NCSe)2(C6H7NO)3] (1) and [Co(NCSe)2(C6H7NO)4] (2) from the same reaction mixture. The asymmetric unit of 1 is built up of one CoII cation, two NCSe− isoselenocyanate anions and three 2-methylpyridine N-oxide coligands, with all atoms located on general positions. The asymmetric unit of 2 consists of two cobalt cations, four isoselenocanate anions and eight 2-methylpyridine N-oxide coligands in general positions, because two crystallographically independent complexes are present. In compound 1, the CoII cations are fivefold coordinated to two terminally N-bonded anionic ligands and three 2-methylpyridine N-oxide coligands within a slightly distorted trigonal–bipyramidal coordination, forming discrete complexes with the O atoms occupying the equatorial sites. In compound 2, each of the two complexes is coordinated to two terminally N-bonded isoselenocyanate anions and four 2-methylpyridine N-oxide coligands within a slightly distorted cis-CoN2O4 octahedral coordination geometry. In the crystal structures of 1 and 2, the complexes are linked by weak C—H...Se and C—H...O contacts. Powder X-ray diffraction reveals that neither of the two compounds were obtained as a pure crystalline phase.