Synthesis, Structures, Polymorphism, and Magnetic Properties of Transition Metal Thiocyanato Coordination Compounds

Reaction of manganese, iron, and nickel thiocyanate with 4-ethylpyridine leads to the formation of single crystals of compounds with composition M(NCS)(2)(L)(4) (1), M(NCS)(2)(L)(2)(H2O)(2) (2-Mn), and M(NCS)(2)(L)(2) (3) with M = Mn, Fe, and Ni and L = 4-ethylpyridine. For most compounds, different polymorphic modifications are observed, and their transition behavior and thermodynamic stability was investigated. Additionally, compounds of composition M(NCS)(2)(L)(2) (M = Mn or Ni) were prepared from solution and by thermal decomposition of compounds 1 and 2, which lead to different stable and metastable modifications. The crystal structures of most compounds were determined by single crystal X-ray diffraction and some of them by Rietveld refinements. Compounds 1 and 2 consist of octahedrally coordinated discrete complexes with terminal N-bonded thiocyanato anions. In compounds 3, the metal cations are linked by pairs of mu-1,3-bridging thiocyanato anions into chains. Surprisingly, thermal decomposition of Ni(NCS)(2)(4-ethylpyridine)(4) leads to the formation of a new compound of composition Ni(NCS)(2)(4-ethylpyridine) (4-Ni). Magnetic measurements reveal that 3-Mn/II and 3-Mn/III show antiferromagnetic ordering at T-N = 21.5 and 23.9 K and that 4-Ni is a metamagnet with a critical field of 1.4 kOe at 2 K. All other compounds show Curie or Curie-Weiss behavior with no magnetic anomalies.