Article,
Exploration and synthesis of condensed coordination networks with modified magnetic properties
CrystEngComm, 15 (5): 945--957 (2013)
DOI: 10.1039/c2ce26617b
Abstract
Eight new coordination polymers based on Ni(NCS)2 and 2-methylpyrazine were discovered, structurally characterized and most of them investigated for their thermal and magnetic properties. In the crystal structures of Ni(NCS)2(2-methylpyrazine)4 (1), Ni(NCS)2(2-methylpyrazine)4middle dot2-methylpyrazine solvate (2) and Ni(NCS)2(2-methylpyrazine)4middle dotethanol solvate (3), the nickel(ii) cations are always octahedral coordinated by two terminal N-bonded thiocyanato anions and four N-bonded 2-methylpyrazine ligands into discrete complexes. The crystal structures of Ni(NCS)2(2-methylpyrazine)2(H2O)2 (4) and Ni(NCS)2(2-methylpyrazine)2(CH3OH)2 (5) also consist of discrete complexes, but in contrast to compounds 1-3 two terminal bonded 2-methylpyrazine ligands are exchanged by two water and methanol molecules, respectively. In Ni(NCS)2(2-methylpyrazine)3(H2O)middle dotNi(NCS)2(2-methylpyrazine)4 (6) two different complexes are observed, in which one nickel(ii) cation is coordinated by two terminal N-bonded thiocyanato anions, three 2-methylpyrazine ligands and one water molecule, whereas the second cation is coordinated by two terminal N-bonded thiocyanato anions and four 2-methylpyrazine ligands. Compounds 2, 3, 4 and 5 transformed into a 2-methylpyrazine deficient 1 : 2 (1 : 2 = ratio between metal and 2-methylpyrazine) compound with the composition Ni(NCS)2(2-methylpyrazine)2 (7) on heating. On further heating this compound subsequently transformed into a 1 : 1 compound with the composition Ni(NCS)2(2-methylpyrazine)n (8). Compound 7 can only be prepared by thermal decomposition and therefore, its structure was solved ab initio from X-ray powder data. It consists of Ni(NCS)2 dimers that are small mu -1,3-bridged by single thiocyanato anions into layers. Single crystal structure analysis of compound 8 proves that nickel(ii) cations are linked by the thiocyanato anions into Ni-(NCS)2-Ni double chains, which are further connected by the 2-methylpyrazine ligands into layers. Magnetic measurements on compounds 2, 3, 4 and 5 show only Curie or Curie-Weiss paramagnetism, whereas in the ligand-deficient compound 7 metamagnetic behavior is observed. The results of these investigations are discussed and compared with those obtained for related coordination compounds with e.g. pyrazine and pyridine as neutral co-ligands.
