Received 7 June 2013
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-HF contacts with adjacent C5H9N2+ cations, resulting in the formation of layers parallel to the ac plane. In (Ia), the C-HF contacts are generally longer and result in the formation of layers along the bc plane.
For the structure of the previously reported polymorph of (I) and its solvatomorph 6C5H9N2+·3SiF62-·CH3OH, see: Light et al. (2007) and Tian et al. (2013), respectively. For an overview of polymorphism, see: Bernstein (2002); Linden (2011). For the practical importance of sterically non-hindered 1,3-dialkyl-1H-imidazolium salts with perfluoro anions of the main-group elements in the preparation of Arduengo carbene adducts, see: Tian et al. (2012). For graph-set notation, see: Etter et al. (1990); Bernstein et al. (1995); Grell et al. (1999).
Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: SHELXTL and OLEX2.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LD2107 ).
Financial support from the National Natural Science Foundation of China (project Nos. 20702041 and 21072157) and the Shaanxi Province Administration of Foreign Experts Bureau Foundation (grant No. 20106100079) is gratefully acknowledged. The authors are thankful to Mr Su Pengfei (Xi'an Modern Chemistry Research Institute) for his help in carrying out the X-ray diffraction measurements.
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