SO Solvation in the 1-Ethyl-3-Methylimidazolium Thiocyanate Ionic Liquid by Incorporation into the Extended Cation-Anion Network.

We have carried out an ab initio molecular dynamics study on the sulfur dioxide (SO) solvation in 1-ethyl-3-methylimidazolium thiocyanate for which we have observed that both cations and anions play an essential role in the solvation of SO. Whereas, the anions tend to form a thiocyanate- and much less often an isothiocyanate-SO adduct, the cations create a "cage" around SO with those groups of atoms that donate weak interactions like the alkyl hydrogen atoms as well as the heavy atoms of the [Formula: see text]-system. Despite these similarities between the solvation of SO and CO in ionic liquids, an essential difference was observed with respect to the acidic protons. Whereas CO avoids accepting hydrogen bonds form the acidic hydrogen atoms of the cations, SO can from O(SO)-H(cation) hydrogen bonds and thus together with the strong anion-adduct it actively integrates in the hydrogen bond network of this particular ionic liquid. The fact that SO acts in this way was termed a linker effect by us, because the SO can be situated between cation and anion operating as a linker between them. The particular contacts are the H(cation)[Formula: see text]O(SO) hydrogen bond and a S(anion)-S(SO) sulfur bridge. Clearly, this observation provides a possible explanation for the question of why the SO solubility in these ionic liquids is so high.