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 σ-donor ligands for stable metal complexes. The title salt, 1,3-bis(4-hydroxyphenyl)-1H-imidazol-3-ium chloride (IOH·Cl), C₁₅H₁₃N₂O₂⁺·Cl^-, is a new imidazolium salt with a hydroxy functionality. The synthesis of IOH·Cl 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 IOH·Cl consists of a central planar imidazolium ring (r.m.s. deviation = 0.001514;Å), with out-of-plane phenolic side arms. The dihedral angles between the 4-hydroxyphenyl substituents and the imidazole ring are 55.2714;(7) and 48.8514;(11)°. In the crystal, O-H..Cl 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-,-y +, z-), with donor-acceptor distances of 2.97714;(2) and 3.013014;(18)14;Å, respectively. The phenolic rings are each π-π stacked with their respective inversion-related [(-x + 1,-y + 1,-z + 1) and (-x,-y + 1,-z + 1)] counterparts, with interplanar distances of 3.56014;(3) and 3.77814;(3)14;Å. The only other noteworthy intermolecular interaction is an O..O (not hydrogen bonded) close contact of 2.99914;(3)14;Å between crystallographically different hydroxy O atoms on translationally adjacent molecules (x + 1, y, x + 1).