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

Abstract

Reaction\nof manganese, iron, and nickel thiocyanate with 4-ethylpyridine\nleads to the formation of single crystals of compounds with composition\nM­(NCS)₂(L)₄ (<b>1</b>), M­(NCS)₂(L)₂(H₂O)₂ (<b>2-Mn</b>),\nand M­(NCS)₂(L)₂ (<b>3</b>) with M = Mn,\nFe, and Ni and L = 4-ethylpyridine. For most compounds, different\npolymorphic modifications are observed, and their transition behavior\nand thermodynamic stability was investigated. Additionally, compounds\nof composition M­(NCS)₂(L)₂ (M = Mn or Ni) were\nprepared from solution and by thermal decomposition of compounds <b>1</b> and <b>2</b>, which lead to different stable and metastable\nmodifications. The crystal structures of most compounds were determined\nby single crystal X-ray diffraction and some of them by Rietveld refinements.\nCompounds <b>1</b> and <b>2</b> consist of octahedrally\ncoordinated discrete complexes with terminal N-bonded thiocyanato\nanions. In compounds <b>3</b>, the metal cations are linked\nby pairs of μ-1,3-bridging thiocyanato anions into chains. Surprisingly,\nthermal decomposition of Ni­(NCS)₂(4-ethylpyridine)₄ leads to the formation of a new compound of composition Ni­(NCS)₂(4-ethylpyridine) (<b>4-Ni</b>). Magnetic measurements\nreveal that <b>3-Mn/II</b> and <b>3-Mn/III</b> show antiferromagnetic\nordering at <i>T</i>_N = 21.5 and 23.9 K and that <b>4-Ni</b> is a metamagnet with a critical field of 1.4 kOe at 2\nK. All other compounds show Curie or Curie–Weiss behavior with\nno magnetic anomalies.