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Abstract

Reaction of Co(NCS)(2) with 2,6-dimethylpyrazine (2,6-DMPy) leads to the formation of a compound with the composition Co (NCS)(2)(2,6-DMPy)(4) (Co-0D) that consists of discrete complexes, in which the Co cations are octahedrally coordinated. Upon heating, half of the 2,6-DMPy ligands are removed leading to the two-dimensional coordination polymer [Co(NCS)(2)(2,6-DMPy)(2)] (Co-2D), shown by thermogravimetry and X-ray powder diffraction. On further heating, the intermediate Co-2D loses the next 2,6-DMPy ligand and transforms into [Co(NCS)(2)(2,6-DMPy)](n) (Co-3D). The crystal structures of Co-2D and Co-3D were solved and refined using powder X-tay diffraction data. The crystal structure of Co-2D consists of octahedrally coordinated Co cations that are linked by pairs of anionic ligands into dimers, which are further connected by single thiocyanate anions into layers. In Co-3D, octahedrally and tetrahedrally coordinated Co-cations are present, that are linked by mu-1,3-bridging single thiocyanate anions into a novel three-dimensional network. Magnetic, measurements for Co-0D show paramagnetic behavior and slow relaxations of the magnetization in an applied field due to single: ion magnet behavior. For Co-2D the antifertomagnOic exchange interaction leads to the maximum of susceptibility at 6.0 K, but a long-range ordering is observed at 2.2 K. In contrast, the ferromagnetic order is observed in Co-3D below 3.75 K.,The phase transitions are invstigated by specific heat measurements.