Polymorphism in Tetramethylammonium Selenocyanate – Crystal Structures of α ‐, β ‐, and γ ‐[NMe 4 ][SeCN]

In the solid state, tetramethylammonium selenocyanate, [NMe 4 ][SeCN], is polymorphic. α ‐[NMe 4 ][SeCN] crystallizes in the monoclinic system with space group P 2 1 / c (at 100 K, No. 14, a = 7.8656(5) Å, b = 8.6002(4) Å, c = 11.9513(8) Å, β = 95.374(5)°, V = 802.15(3) Å 3 ), β ‐[NMe 4 ][SeCN] with space group Pnma (at 348 K, No. 62, a = 12.1914(12) Å, b = 7.7491(8) Å, c = 8.9840(8) Å, V = 848.74(14) Å 3 ), and γ ‐[NMe 4 ][SeCN] with space group Pmmn (at 388 K, No. 59, a = 7.529(2) Å, b = 9.586(3) Å, c = 5.9535(18) Å, V = 429.68(20) Å 3 ). All structures are related by direct group‐subgroup relationships, which are shown with the Bärnighausen formalism. Furthermore, all [NMe 4 ][SeCN] polymorphs, as well as some related compounds, share the CsCl‐type as the common aristotype.