Crystal structure and aggregation behavior in water of ionic liquid 1-hexadecyl-3-methylimidazolium Bromide

A large-transparent single crystal of 1-hexadecyl-3-methylimidazolium bromide monohydrate ([C₁₆mim]Br·H₂O) with 4-mm length was firstly obtained in the water-trichloromethane-toluene growth system (V_water:V_{trichloromethane}:V_toluene = 0.1:1:2). The crystal structure was determined by single crystal X-ray diffraction method. It crystallizes in the triclinic system, space group P-1, with unit cell parameters a = 5.4962(15) Å, b = 7.839(2) Å, c = 27.279(8) Å, α = 94.375°(4), β = 91.500°(5), γ = 101.999°(4), Z = 2, V = 1145.2(5)ų, Dc = 1.176 Mg/m³, μ = 1.804 mm^{- 1}, F(000) = 436, the final R1 = 0.0497, wR2 = 0.1154. The 3D supramolecular structure is constructed through the weak interactions between imidazolium cations, Br^- anions and lattice water molecules. The long alkyl chain to imidazolium ring and lattice water molecules play an important role in the self-assembled process. Moreover, it is proposed that [C₁₆mim]Br has the aggregation behavior in water at the higher concentration and the possible self-assembled structure is the interdigitated pattern.