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-hy-droxy-phen-yl)-1H-imidazol-3-ium chloride (IOH·Cl), C15H13N2O2 +·Cl-, is a new imidazolium salt with a hy-droxy functionality. The synthesis of IOH·Cl was achieved in high yield via a two-step procedure involving a di-aza-butadiene precursor followed by ring closure using tri-methylchloro-silane and paraformaldehyde. The structure of IOH·Cl consists of a central planar imidazolium ring (r.m.s. deviation = 0.0015 Å), with out-of-plane phenolic side arms. The dihedral angles between the 4-hy-droxy-phenyl substituents and the imidazole ring are 55.27 (7) and 48.85 (11)°. In the crystal, O-H⋯Cl hydrogen bonds connect the distal hy-droxy 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 2.977 (2) and 3.0130 (18) 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 inter-planar distances of 3.560 (3) and 3.778 (3) Å. The only other noteworthy inter-molecular inter-action is an O⋯O (not hydrogen bonded) close contact of 2.999 (3) Å between crystallographically different hy-droxy O atoms on translationally adjacent mol-ecules (x + 1, y, x + 1).
Keywords: Hirshfeld surface; N-heterocyclic carbene; crystal structure; hydrogen bonding; imidazolium salt.