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 crystal structures of the title compounds, which arose from the same reaction, consist of discrete complexes in which the cobalt cations are either in a CoN₂O₃ trigonal–bipyramidal or a CoN₂O₄ octa­hedral coordination.

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 Co^II 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 Co^II 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.