Crystal structure of zwitterionic 3,3'-[1,1'-(butane-1,4-di-yl)bis-(1H-imidazol-3-ium-3,1-di-yl)]bis-(propane-1-sulfonate) dihydrate.

The crystal structure of the title compound, C16H26N4O6S2·2H2O, a water-soluble di-N-heterocyclic carbene ligand precursor was determined using a single crystal grown by the slow cooling of a hot N,N-di-methyl-formamide solution of the compound. The dihydrate crystallizes in the monoclinic space group P21/c, with half of the zwitterionic mol-ecule and one water mol-ecule of crystallization in the asymmetric unit. The remaining part of the mol-ecule is completed by inversion symmetry. In the mol-ecule, the imidazole ring planes are parallel with a plane-to-plane distance of 2.741 (2) Å. The supra-molecular network is consolidated by hydrogen bonds of medium strength between the zwitterionic mol-ecules and the water mol-ecules of crystallization, as well as by π-π stacking inter-actions between the imidazole rings of neighbouring mol-ecules and C-H⋯O hydrogen-bonding inter-actions.