Trichlorido(1,3-dimethyl-2,3-di­hydro-1H-imidazol-2-yl­idene-κC²)aluminium(III)

The title compound, [Al(C₅H₈N₂)Cl₃], was prepared by a thermolytic decomposition under high-vacuum conditions and presents a formal adduct of an Arduengo carbene, 1,3-dimethyl-1H-imidazol-2-yl­idene, and aluminium trichloride. The Al atom adopts a pseudo-tetra­hedral CCl₃ coordination environment. All N and C atoms, the Al atom, one of the Cl atoms, and all aromatic H atoms of the mol­ecule lie on a mirror plane. As a result of the mirror symmetry of the mol­ecule, the H atoms of all methyl groups are disordered between symmetry-equivalent positions.

Bis(1,3-dimethyl-1H-imidazolium) hexa­fluoro­silicate methanol 0.33-solvate

The title compound, 6C₅H₉N₂⁺·3SiF₆²⁻·CH₃OH, (I), was prepared by recrystallization of the crude salt from methanol along with solvent-free 2C₅H₉N₂⁺·SiF₆²⁻ (II). Crystals of these solvatomorphs can be separated manually. The solvate (I) crystallizes in a rare hexa­gonal space group P6/mcc. Its asymmetric unit comprises one half of an imidazolium cation bis­ected by the crystallographic m-plane, one-sixth and one-twelfth of two crystallographically independent SiF₆^2– dianions (Si atoms are located on the 3.2 and 6/m inversion centres), and one-twelfth of a methanol mol­ecule (C atoms are situated on the 622 inversion centres, other atoms are disordered between general positions). In (I), all F atoms of 3.2-located SiF₆^2– dianions participate in the formation of symmetry-equivalent contacts to the H atoms of imidazolium fragments, thus forming rod-type ensembles positioned on the -6 axes. These `pillar' rods are, in turn, F...H inter­linked through SiF₆^2– dianions disordered around the 6/m centres. The twelvefold disordered methanol mol­ecules are appended to this array by O—H...F hydrogen bonds to the 6/m located SiF₆^2– dianions. In terms of graph-set notation, the first and second level networks in (I) are N₁ = C₂²(7)[3R₄⁴(14)]D₂²(4) and N₂ = D₂²(5) (C—H...O hydrogen bonds are not considered). After locating all symmetrically independent atoms in the cation and anions, there remained a strong (> 3 e Å⁻³) residual electron density peak located at the 622 inversion centre. Treatment of this pre-refined model with the SQUEEZE procedure in PLATON [Spek (2009). Acta Cryst. D65, 148–155] revealed two voids per unit cell, indicative of the presence of the solvent methanol mol­ecule disordered about the 622 inversion centre.

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

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 SiF₆^2– 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.