Molecular Structure of N-Methylbis (2-Hydroxyethyl)Ammonium hexafluorosilicate at 100 and 298 K

Two polymorphic modifications of N-methylbis(2-hydroxyethyl)ammonium hexafluorosilicate (AHFS) crystallize in monoclinic symmetry. The independent part of the unit cell of the low temperature modification contains two cations and an anion. The cell volume is two times smaller in the high temperature modification, the [SiF 6 ] 2- anion being disordered. In both modifications of methylbis(2-hydroxyethyl)ammonium hexafluorosilicate (HOCH 2 CH 2 ) 2 HN + [SiF 6 ] 2- , the [SiF 6 ] 2- anion and the (HOCH 2 CH 2 ) 2 HN + CH 3 cation are linked by F…H—O hydrogen bonds. The silicon atom polyhedron in the anion is a tetragonal bipyramid; the coordination polyhedron of the nitrogen atom in the cation is a tetrahedron.