Effect of methyl-ene versus ethyl-ene linkers on structural properties of tert-butyl and mesityl bis-(imidazolium) bromide salts.

The crystal structures of ligand precursor bis-(imidazolium) salts 1,1'-methyl-enebis(3-tert-butyl-imidazolium) dibromide monohydrate, C15H26N4 +·2Br-·H2O or [ tBuNHC2Me][Br]2·H2O, 1,1'-(ethane-1,2-di-yl)bis-(3-tert-butyl-imidazolium) dibromide dihydrate, C16H28N4 +·2Br-·2H2O or [ tBuNHC2Et][Br]2·2H2O, 1,1'-methyl-enebis[3-(2,4,6-tri-methyl-phen-yl)imidazolium] dibromide dihydrate, C25H30N4 2+·2Br-·2H2O or [MesNHC2Me][Br]2·2H2O, and 1,1'-(ethane-1,2-di-yl)bis-[3-(2,4,6-tri-methyl-phen-yl)imidazolium] dibromide tetra-hydrate, C26H32N4 2+·2Br-·4H2O or [MesNHC2Et][Br]2·4H2O, are reported. At 293 K, [ tBuNHC2Me][Br]2·H2O crystallizes in the P21/c space group, while [ tBuNHC2Et][Br]2·2H2O crystallizes in the P21/n space group at 100 K. At 112 K, [MesNHC2Me][Br]2·2H2O crystallizes in the ortho-rhom-bic space group Pccn while [MesNHC2Et][Br]2·4H2O crystallizes in the P21/c space group at 100 K. Bond distances and angles within the imidazolium rings are generally comparable among the four structures. All four bis-(imidazolium) salts co-crystallize with one to four mol-ecules of water.