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Acta Cryst. (2013). E69, o1218-o1219  [ doi:10.1107/S1600536813018242 ]

Bis(1,3-dimethyl-1H-imidazolium) hexafluorosilicate: the second monoclinic polymorph

C. Tian, W. Nie and M. V. Borzov

Abstract: The title compound, 2C5H9N2+·SiF62-, (I), crystallized as a new polymorph, different from the previously reported one (Ia) [Light et al. (2007) private communication (refcode: NIQFAV). CCDC, Cambridge, England]. The symmetry [space groups P21/n for (I) and C2/c for(Ia)] and crystal packing patterns are markedly different for this pair of polymorphs. In (I), all imidazolium cations in the lattice are nearly parallel to each other, whereas a herringbone arrangement can be found in (Ia). In (I), each SiF62- dianion forms four short C-H...F contacts with adjacent C5H9N2+ cations, resulting in the formation of layers parallel to the ac plane. In (Ia), the C-H...F contacts are generally longer and result in the formation of layers along the bc plane.

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