The Influence of the Halide in the Crystal Structures of 1-(2,3,5,6-Tetrafluoro-4-pyridyl)-3-benzylimidazolium Halides

The crystal structures of 1-(2,3,5,6-tetrafluoro-4-pyridyl)-3-benzylimidazolium chloride (1) and iodide (3) have been determined by single crystal X-ray diffraction. The crystal structure of 1 is similar to that of the bromide salt (2), possessing anion···C(5)F(5)N···C(6)H(5) motifs, whilst that of 3 contains columns of alternating iodide anions and parallel tetrafluoropyridyl rings. All three crystal structures possess C(1)–H∙∙∙X(−) and C(2)–H∙∙∙X(−) hydrogen bonding. DFT calculations reveal that the strengths of the hydrogen bonding interactions lie in the order C(1)–H···X(−) > C(3)–H···X(−) > C(2)–H···X(−) for the same halide (X(−)) and Cl(−) > Br(−) > I(−) for each position. It is suggested that salt 3 adopts a different structure to salts 1 and 2 because of the larger size of iodide.