Liquid Crystals of N,N‘-Dialkylimidazolium Salts Comprising Palladium(II) and Copper(II) Ions

Metal-containing ionic liquid crystals of N,N‘-dialkylimidazolium salts of Pd^II and Cu^II ([(C_nH_2n+1)₂-im][MCl₄], n = 8, 10, 12, 14, 16, and 18 for M = Pd^II and n = 10, 12, 14, 16, and 18 for M = Cu^II) were prepared. Crystal structures of two compounds, [(C₁₂H₂₅)₂-im]₂[PdCl₄] and [(C₁₂H₂₅)₂-im]₂[CuCl₄]·H₂O, have been characterized by single crystal X-ray diffraction. The cations of these two compounds adopt a U-shaped conformation and are packed in a highly interdigitated bilayer fashion. The square planar PdCl₄^2- and distorted tetrahedral CuCl₄^2- are sandwiched between the cationic bilayers individually. Both series of compounds exhibit a wide temperature range of SmA mesophase. Thermal decompositions are observed near the clearing tempertures. For the Pd^II series, decomposition generates palladium dicarbene and carbene-imidazole complexes. Ionic liquid crystals with different combinations of [(C₁₈H₃₇)₂-im]₂[PdCl₄], [(C₁₈H₃₇)₂-im]₂[CuCl₄]·H₂O, and [(C₁₈H₃₇)₂-im]Cl·H₂O are good candidates for Pd^II/Cu^II catalyzed reactions carried out under partially ordered environments of ionic liquids.