Crystal structure of bis(imidazolium) para-toluenesulfonate, C20H22N4O6S2

Abstract

Source of materialThecompoundwas prepared upon reacting the neutral nitrogencontaining compound with iron(III)-para-toluenesulfonatehexahydrate in methanol. Crystals suitable for the diffraction study were obtained upon evaporation of the solvent at ambient conditions. Experimental detailsCarbon-bound Hatomswere placed in calculated positions (C-H 0.95 Å) and were included in the refinementinthe riding model approximation, with U iso (H) setto1.2U eq (C). The Hatoms of the methyl group were allowed to rotate with afixed angle around the C-C bond to best fit the experimental electron density (HFIX 137 in the SHELX program suite [10]), with U iso (H) setto1.5U eq (C). Nitrogen-bound Ha tomsw ere placed in calculated positions (N-H 0.88 Å) and were included in the refinement in the riding model approximation, with U iso (H) setto1.2U eq (N). DiscussionPerfluorinated hydrocarbons ionic liquids have attracted much attention as versatilereactionmedia over thepast decades. Aprerequisitefor the suitability of asalttoact as ionic liquid is its low melting pointthat is conveniently achieved by the introduction of long perfluoroalkylalkyl chainsinto simple nitrogen-containing organic moieties and crystallizing theresulting cations by means of bulkier anions suchastosylate [1]. In our continued interest in creating simplerd erivatives of nitrogen compounds that might act as ionicliquids [2] motivated us to synthesize the title compound andelucidateits crystal structure by means of adiffraction study. Exampleso fi midazolium-baseds ulfonates haveb een characterized structurallybefore [3][4][5].The title compoundisthe para-toluene-sulfonatesalt of bisimidazole.The asymmetric unit contains half ac ation and ac omplete anion. Thel east-squares planes as defined by the non-hydrogen atomso ft he two heterocyclic moieties, respectively the phenylgroup on the one hand and one of the heterocy-clic rings on the other hand, intersect at an angle of 84.48(4)°. Intracyclic angles in the cation span arange of 106.93(11)-108.99(11)°with the smallest angle found on one of the "terminal" carbon atomsand the largest angle on one of the nitrogen atoms. The S-O bond lengths are measured in between 1.4355(10)-1.4738(11) Åw ith the shortest bond length observed for the oxygen atom that does not participate in any intermolecu-larc ontacts( videi nfra). In comparisont oo ther tosylateswhose metricalparameters have been deposited with the Cambridge Structural Database [6],t hese values are in good agreementwiththe most commonones observed. In the crystal, classical hydrogen bonds of the N-H×××Otype are observed next to C-H×××Ocontacts whose range invariably falls below the sum of van-der-Waals radii of the atomsparticipating in them [7].The classical hydrogen bonds involve all NH groups as donors and are directed towards two different oxygen atomsofthe tosylate anion as acceptors.The C-H×××Ocontacts are supported by one of the CH groups of the cation and -exclusively -only have one of the two oxygen atomsasacceptors that is also engaged in the clas...