Ca(SCN)2 and Ca(SCN)2 · 2 H2O: Crystal Structure, Thermal Behavior and Vibrational Spectroscopy
2014
Wickleder, Claudia | Larsen, Patrick
The dehydration of Ca(SCN)₂∙4H₂O yields single crystals of Ca(SCN)₂ ∙ 2 H₂O as well as of Ca(SCN)₂. Ca(SCN)₂ ∙ 2 H₂O crystallizes with a hitherto unknown structure (orthorhombic, Pnma, Z = 4, a = 1280.1(2), b = 790.3(1), c = 726.9(1) pm, Rₐₗₗ = 0.0430). The Ca²⁺ ions are surrounded by four SCN⁻ ions and four water molecules. The polyhedra are connected to chains along [010] via common oxygen atoms. The SCN⁻ ions connect these chains to a three-dimensional network so that each thiocyanate group is linked to two Ca²⁺ ions. Hydrogen bonding with sulfur atoms as acceptors is observed. The crystal structure of Ca(SCN)₂ (monoclinic, C2/c, Z = 4, a = 961.7(2), b = 642.4(2), c = 787.2(2) pm, Rₐₗₗ = 0.0673) consists of alternating layers of Ca²⁺ and SCN⁻ ions. The cations are surrounded by four sulfur and four nitrogen atoms in form of a square antiprism. According to ³∞[Ca(SCN)₈/₄] each SCN⁻ ion connects four Ca²⁺ ions with each other. Thermal investigations show a phase transition of Ca(SCN)₂ ∙ 4 H₂O followed by dehydration to Ca(SCN)₂ which finally decomposes yielding CaS. IR and Raman measurements have been performed and the resulting frequencies assigned and discussed.
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