Synthesis and crystal structure of 1,3-bis­­(4-hy­dr­oxy­phen­yl)-1H-imidazol-3-ium chloride

Imidazolium salts are common building blocks for functional materials and in the synthesis of N-heterocyclic carbene (NHC) as -donor ligands for stable metal complexes. The title salt, 1,3-bis(4-hydroxyphenyl)-1H-imidazol-3-ium chloride (IOHCl), C15H13N2O2 Cl, is a new imidazolium salt with a hydroxy functionality. The synthesis of IOHCl was achieved in high yield via a two-step procedure involving a diazabutadiene precursor followed by ring closure using trimethylchlorosilane and paraformaldehyde. The structure of IOHCl consists of a central planar imidazolium ring (r.m.s. deviation = 0.0015 A˚ ), with out-ofplane phenolic side arms. The dihedral angles between the 4-hydroxyphenyl substituents and the imidazole ring are 55.27 (7) and 48.85 (11). In the crystal, O—HCl hydrogen bonds connect the distal hydroxy groups and Cl anions in adjacent asymmetric units, one related by inversion (x + 1, y + 1, z + 1) and one by the n-glide (x 1 2, y + 1 2, z 1 2), with donor–acceptor distances of 2.977 (2) and 3.0130 (18) A˚ , respectively. The phenolic rings are each – stacked with their respective inversion-related [(x + 1, y + 1, z + 1) and (x, y + 1, z + 1)] counterparts, with interplanar distances of 3.560 (3) and 3.778 (3) A˚ . The only other noteworthy intermolecular interaction is an OO (not hydrogen bonded) close contact of 2.999 (3) A˚ between crystallographically different hydroxy O atoms on translationally adjacent molecules (x + 1, y, x + 1).