1. 3,3'-Di-n-butyl-1,1'-(p-phenyl-ene-dimethyl-ene)diimidazolium bis-(hexa-fluoro-phosphate)
Rosenani A Haque, Abbas Washeel, S Fatimah Nasri, Chin Sing Yeap, Hoong-Kun Fun Acta Crystallogr Sect E Struct Rep Online. 2010 Mar 13;66(Pt 4):o824-5. doi: 10.1107/S1600536810008536.
The asymmetric unit of the title N-heterocyclic carbene compound, C(22)H(32)N(4) (2+)·2PF(6) (-), consists of one half of the N-heterocyclic carbene dication and one hexa-fluoro-phosphate anion. The dication lies across a crystallographic inversion center. The imidazole ring is twisted away from the central benzene ring, making a dihedral angle of 76.23 (6)°. The hexa-fluoro-phosphate anions link the cations into a three-dimensional network via inter-molecular C-H⋯F hydrogen bonds. A weak C-H⋯π inter-action further stabilizes the crystal structure.
2. 1,1'-[(1,3-Dihydroxypropane-2,2-diyl)dimethylene]dipyridinium bis-(hexa-fluoro-phosphate)
Ai-Lin Yuan, Chun-Ling Zheng, Ling-Hua Zhuang, Chang-Sheng Wang, Guo-Wei Wang Acta Crystallogr Sect E Struct Rep Online. 2011 May 1;67(Pt 5):o1104. doi: 10.1107/S1600536811013080. Epub 2011 Apr 13.
The title compound, C(15)H(20)N(2)O(2) (2+)·2PF(6) (-), was prepared by anion exchange of two bromide ions in the ionic liquid 2,2'-bis-(pyridinium-1-ylmeth-yl)-propane-1,3-diol dibromide with potassium hexa-fluoro-phosphate. The two pyridine rings are planar (r.m.s. deviations = 0.008 and 0.00440 Å) and make a dihedral angle of 44.0 (2)°. Intermolecular O-H⋯F and C-H⋯F interactions occur. The four F atoms in each anion were refined as disordered over two sets of sites with an occupancy ration of 0.700 (19):0.300 (19).
3. 3,3'-Dimethyl-1,1'-(butane-1,4-di-yl)diimidazolium bis-(tetra-fluoro-borate)
Hao Geng, Ling-Hua Zhuang, Jian Zhang, Guo-Wei Wang, Ai-Lin Yuan Acta Crystallogr Sect E Struct Rep Online. 2010 May 8;66(Pt 6):o1267. doi: 10.1107/S160053681001593X.
The title compound, C(12)H(20)N(4) (2+)·2BF(4) (-), was prepared by the anion exchange of a dibromide ionic liquid with sodium tetra-fluoro-borate. The asymmetric unit contains one half of the imidazolium cation, which lies about an inversion centre at the mid-point of the central C-C bond of the linking butyl chain. The two planar imidazole rings (r.m.s. deviation = 0.0013 Å) are strictly parallel and separated by 2.625 (7) Å [vertical distance between the centroids of two imidazole rings], giving the mol-ecule a stepped appearance. In the crystal structure, inter-molecular C-H⋯F hydrogen bonds link the cations and anions, generating a three-dimensional network.
