Structures and Magnetic Properties of Nickel Thiocyanato Coordination Compounds with 2-Chloropyrazine as a Neutral Coligand



Reaction of Ni(NCS)2 with 2-chloropyrazine in different molar ratios and solvents at room temperature leads to five new coordination polymers. In the crystal structures of Ni(NCS)2(2-chloropyrazine)4·2-chloropyrazine solvate (1) and Ni(NCS)2(2-chloropyrazine)4 (2) the nickel cations are octahedrally coordinated by two terminal N-bonded thiocyanato anions and four 2-chloropyrazine ligands into discrete complexes. In the crystal structures of the Ni(NCS)2(2-chloropyrazine)2(CH3OH)2·(CH3OH)2 solvate (3) and Ni(NCS)2(2-chloropyrazine)2(CH3OH)2 (4) each nickel(II) cation is coordinated by two terminal N-bonded thiocyanato anions, two 2-chloropyrazine ligands and two O-bonded methanol molecules in a slightly distorted octahedron. On heating, compounds 1 and 2 transform into the ligand-deficient 1:2 compound 5, which can also be crystallized from solution. In the crystal structure of [Ni(NCS)2(2-chloropyrazine)2]n (5) each nickel(II) cation is coordinated by two N-bonded and two S-bonded thiocyanato anions as well as two 2-chloropyrazine ligands. The nickel cations are linked into dimers by pairs of μ-1,3-bridging thiocyanato anions that are further linked into chains and finally into layers by single μ-1,3-bridging thiocyanato anions. Magnetic measurements of compound 1 and 2 show only Curie or Curie–Weiss paramagnetism, whereas in the ligand-deficient compound 5 a metamagnetic transition is observed at a critical field of HC = 14 kOe. The results of the magnetic measurements are compared with those of related nickel compounds with different coligands.