X-ray diffraction study of ionic liquid based mixtures.

Crystal structures in N,N-diethyl-N-methyl-N-2-methoxyethylammonium tetrafluoroborate, [DEME][BF(4)], are determined by X-ray diffraction method. In [DEME][BF(4)]-based mixtures, various kinds of crystal structures and superstructures are induced by additives, i.e., H(2)O, CH(3)OH, C(2)H(5)OH, and C(6)H(6). Most of the crystal structures in the mixtures are related to that of pure [DEME][BF(4)], though unit cells in 1.1 and 6.1 mol % C(6)H(6) are different from the pure one. Further, [DEME][BF(4)]-C(6)H(6) mixtures require the two kinds of superstructures, where volume per [DEME][BF(4)] is contracted by a small amount of additives. Also, volume contraction and the coexistence of two kinds of superstructures are seen in 0.9 mol % H(2)O. The superstructures are derived from orientational or displacive modulations of [DEME][BF(4)] molecules. In spite of a small amount of additives, molecular interactions of [DEME][BF(4)] are influenced extensively.