Effect of methyl­ene versus ethyl­ene linkers on structural properties of tert-butyl and mesityl bis­(imidazolium) bromide salts

The crystal structures of ligand precursor bis­(imidazolium) salts 1,1′-methyl­enebis(3-tert-butyl­imidazolium) dibromide monohydrate, C15H26N4+·2Br−·H2O or [tBuNHC2Me][Br]2·H2O, 1,1′-(ethane-1,2-di­yl)bis­(3-tert-butyl­imidazolium) dibromide dihydrate, C16H28N4+·2Br−·2H2O or [tBuNHC2Et][Br]2·2H2O, 1,1′-methyl­enebis[3-(2,4,6-tri­methyl­phen­yl)imidazolium] dibromide dihydrate, C25H30N42+·2Br−·2H2O or [MesNHC2Me][Br]2·2H2O, and 1,1′-(ethane-1,2-di­yl)bis­[3-(2,4,6-tri­methyl­phen­yl)imidazolium] dibromide tetra­hydrate, C26H32N42+·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 ortho­rhom­bic 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 mol­ecules of water.