Crystal structure of metronidazolium tetra-chlorido-aurate(III)

Metronidazole (MET) [systematic names: 1-(2-hy-droxy-eth-yl)-2-methyl-5-nitro-1H-imidazole and 2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethanol] is a medication that is used to treat infections from a variety of anaerobic organisms. As with other imidazole derivatives, metronidazole is also susceptible to protonation. However, there are few reports of the structures of metronidazolium derivatives. In the title compound, (C6H10N3O3)[AuCl4] [systematic name: 1-(2-hy-droxy-eth-yl)-2-methyl-5-nitro-1H-imidazol-3-ium tetra-chlorido-aur-ate(III)], the asymmetric unit consists of a metronidazolium cation, [H(MET)](+), and a tetra-chlorido-aurate(III) anion, [AuCl4](-), in which the Au(III) ion is in a slightly distorted square-planar coordination environment. In the cation, the nitro group is essentially coplanar with the imidazole ring, as indicated by an O N-C=C torsion angle of -0.2 (4)°, while the hy-droxy-ethyl group is in a coiled conformation, with an O(H)-C-C-N torsion angle of 62.3 (3)°. In the crystal, the anion and cation are linked by an inter-molecular O-H⋯Cl hydrogen bond. In addition, the N-H group of the metronidazolium ion serves as a hydrogen-bond donor to the O atom of the hy-droxy-ethyl group of a symmetry-related mol-ecule, leading to the formation of chains along [010].