Syntheses and crystal structures of the five- and sixfold coordinated complexes diiso-seleno-cyanato-tris-(2-methyl-pyridine -oxide)cobalt(II) and diiso-seleno-cyanato-tetra-kis-(2-methyl-pyridine -oxide)cobalt(II).

The reaction of CoBr, KNCSe and 2-methyl-pyridine -oxide (CHNO) in ethanol leads to the formation of crystals of [Co(NCSe)(CHNO)] () and [Co(NCSe)(CHNO)] () from the same reaction mixture. The asymmetric unit of is built up of one Co cation, two NCSe iso-seleno-cyanate anions and three 2-methyl-pyridine -oxide coligands, with all atoms located on general positions. The asymmetric unit of consists of two cobalt cations, four iso-seleno-canate anions and eight 2-methyl-pyridine -oxide coligands in general positions, because two crystallographically independent complexes are present. In compound , the Co cations are fivefold coordinated to two terminally N-bonded anionic ligands and three 2-methyl-pyridine -oxide coligands within a slightly distorted trigonal-bipyramidal coordination, forming discrete complexes with the O atoms occupying the equatorial sites. In compound , each of the two complexes is coordinated to two terminally N-bonded iso-seleno-cyanate anions and four 2-methyl-pyridine -oxide coligands within a slightly distorted -CoNO octa-hedral coordination geometry. In the crystal structures of and , 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.