Synthesis, characterization, and crystal structures of four 1,3-diisopropylbenzimidazolium salts with iodide, aluminum tetraiodide, tetrakis[3,5-bis(trifluoromethyl)-phenyl]borate, and triiodide anions

Four 1,3-disubstituted benzimidazolium salts: 1,3-diisopropylbenzimidazolium iodide (1), 1,3-diisopropylbenzimidazolium aluminum tetraiodide (2), 1,3-diisopropylbenzimidazolium triiodide (3), and 1,3-diisopropylbenzimidazolium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (4) have been characterized using single X-ray diffraction analysis. Compounds 2–4 are new and are characterized by NMR and IR spectroscopy. Compound 2 was prepared by reacting 1 with aluminum triiodide and compound 4 in a metathesis reaction of 1 with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, giving yields of 96% and 93%, respectively. Compound 3 was prepared by reacting 1 with 1 eq. of iodine and was isolated in 34% yield. Compound 1 crystallizes in the Orthorhombic space group P2 1 2 1 2 1 with an asymmetric unit consisting of one benzimidazolium cation and one iodine anion. Compound 2 crystallizes in the Monoclinic space group P2 1 / n with an asymmetric unit consisting of one benzimidazolium cation and one aluminum tetraiodide anion. Compound 3 crystallizes in the Monoclinic space group C2/ c with an asymmetric unit consisting of one and one-half benzimidazolium cations and one and one-half triiodide anions. Compound 4 crystallizes in the Triclinic space group P-1 with an asymmetric unit consisting of one benzimidazolium cation and one tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anion. The NCN angles in all four compounds are approximately 110°, which is consistent with literature values. Stacking and halogen and hydrogen bonding interactions in the series are also discussed.