Crystal structures and magnetic properties of the interpenetrating rutile-related compounds M(tcm)2 [M = octahedral, divalent metal; tcm− = tricyanomethanide, C(CN)3−] and the sheet structures of [M(tcm)2(EtOH)2] (M = Co or Ni)

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Abstract
The isomorphous structures of M(tcm)2 [MII = Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd or Hg; tcm– = tricyanomethanide, C(CN)3 –] contain two interpenetrating rutile-related networks generated by octahedral six-connecting metal ions and trigonal three-connecting tcm– anions. The detailed variable temperature and variable field magnetic properties of this series of high-spin complexes generally point to the existence of very weak intraframework coupling with no evidence for long range magnetic order or interframework effects. The compound Cr(tcm)2 is the most strongly coupled and displays a field independent maximum in susceptibility at 14.5 K and a J value of –1.6 cm–1 (using a –2JS1·S2 Heisenberg chain model); Co(tcm)2 displays high temperature magnetic moments typical of essentially uncoupled octahedral centres but with a most unusual field dependence in µCo observed below 10 K, probably due to very weak ferromagnetic coupling, and an Msat value in high fields, at 2 K, which is significantly less than that expected for S = 3/2. Doping of M(tcm)2 with another M′ member of the series leads to a crystal structure isomorphous with M(tcm)2 in which the dopant metal M′ occupies the M site in a random fashion. The resultant magnetism is simply intermediate between those of the parent phases. The isomorphous structures of [M(tcm)2(EtOH)2] (MII = Co or Ni) contain pseudo square-grid sheets in which the tcm– ligands are each co-ordinated to two metal ions and act as a kinked bridge. Each metal is co-ordinated to four tcm– anions in an equatorial arrangement and to two axial ethanol ligands. Extensive intrasheet hydrogen bonding exists between the ethanol molecules and the unco-ordinated nitrile of the tcm– bridges.

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