3,3'-Di-n-propyl-1,1'-(1,3-phenyl-ene-dimethyl-ene)di(1H-imidazol-3-ium) bis-(hexa-fluorophosphate).

In the title compound, C(20)H(28)N(4) (2+)·2PF(6) (-), the dihedral angles between the benzene ring and the imidazole rings are 70.18 (11) and 69.83 (11)°, while the imidazole rings form a dihedral angle of 40.52 (12)°. In the crystal, weak C-H⋯F inter-actions link the mol-ecules into a two-dimensional network parallel to (001). A π-π inter-action with a centroid-centroid distance of 3.601 (1) Šis also observed in the crystal structure.

3,3'-Diethyl-1,1'-(1,4-phenyl-ene-dimethyl-ene)diimidazol-3-ium bis-(hexa-fluoro-phosphate).

In the title mol-ecular salt, C(18)H(24)N(4) (2+)·2PF(6) (-), the complete dication is generated by a crystallographic inversion centre. The central benzene ring makes a dihedral angle of 77.19 (9)° with each of the imidazole rings. In the crystal, C-H⋯F inter-actions link the cations and anions into layers lying parallel to the bc plane. The hexa-fluoro-phosphate anion is disordered over two sets of sites in a 0.520 (11):0.480 (11) ratio.

3,3'-Dicyclo-pentyl-1,1'-(1,3-phenyl-enedimethyl-ene)dibenzimidazol-1-ium bis-(hexa-fluoro-phosphate).

In the title compound, C(32)H(36)N(4) (2+)·2PF(6) (-), the cation and the anions each have crystallographic twofold rotation symmetry. The benzimidazole ring is almost planar [r.m.s. deviation = 0.0161 (1) Å] and makes a dihedral angle of 5.77 (4)° with its symmetry-related component and a dihedral angle of 80.96 (5)° with the central benzene ring. The cyclo-pentyl ring adopts a half-chair conformation. In the crystal, mol-ecules are linked into a three-dimensional network through C-H⋯F hydrogen bonds. A C-H⋯π inter-action is also observed.

3,3'-Di-n-propyl-1,1'-[p-phenyl-enebis(methyl-ene)]diimidazolium dibromide.

The asymmetric unit of the title compound, C(20)H(28)N(4) (2+)·2Br(-), consists of half a 3,3'-di-n-propyl-1,1'-[p-phenyl-enenis(methyl-ene)]diimidazolium cation and a bromide anion. The cation is located on an inversion center and adopts an ⋯AAA⋯ trans conformation. In the crystal, the cation is linked to the anions via weak C-H⋯Br hydrogen bonds.

3,3'-Di-n-butyl-1,1'-(p-phenyl-ene-dimethyl-ene)diimidazolium bis-(hexa-fluoro-phosphate).

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.