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, C 15 H 26 N 4 + ·2Br - ·H 2 O or [ t Bu NHC 2 Me][Br] 2 ·H 2 O, 1,1'-(ethane-1,2-di-yl)bis-(3- tert -butyl-imidazolium) dibromide dihydrate, C 16 H 28 N 4 + ·2Br - ·2H 2 O or [ t Bu NHC 2 Et][Br] 2 ·2H 2 O, 1,1'-methyl-enebis[3-(2,4,6-tri-methyl-phen-yl)imidazolium] dibromide dihydrate, C 25 H 30 N 4 2+ ·2Br - ·2H 2 O or [ Mes NHC 2 Me][Br] 2 ·2H 2 O, and 1,1'-(ethane-1,2-di-yl)bis-[3-(2,4,6-tri-methyl-phen-yl)imidazolium] dibromide tetra-hydrate, C 26 H 32 N 4 2+ ·2Br - ·4H 2 O or [ Mes NHC 2 Et][Br] 2 ·4H 2 O, are reported. At 293 K, [ t Bu NHC 2 Me][Br] 2 ·H 2 O crystallizes in the P 2 1 / c space group, while [ t Bu NHC 2 Et][Br] 2 ·2H 2 O crystallizes in the P 2 1 / n space group at 100 K. At 112 K, [ Mes NHC 2 Me][Br] 2 ·2H 2 O crystallizes in the ortho-rhom-bic space group Pccn while [ Mes NHC 2 Et][Br] 2 ·4H 2 O crystallizes in the P 2 1 / 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.