Hydrogen bonding in the crystal structures of the ionic liquid compounds butyldimethylimidazolium hydrogen sulfate, chloride, and chloroferrate(II,III).

Four ionic liquid (IL) salts containing the 1-butyl-2,3-dimethylimidazolium (BDMIM) and 1-allyl-2,3-dimethylimidazolium (ADMIM) cations have been prepared; the characterization was based on IR spectroscopy and single-crystal structure determination. The compounds BDMIM[HSO4], BDMIMCl, ADMIMBr, and (BDMIM)4[FeIICl4][FeIIICl4]2 were chosen to incorporate anions significantly differing in hydrogen-bond-acceptor strength in order to elucidate the influence of directional bonding on crystal packing. The cations adopt different arrangements with respect to the counterions. The role of hydrogen bonding in these compounds is discussed with respect to its general significance for lattice energies of IL salts.