Synthesis, X-ray structure analysis and density functional study of an unusual anhydrous 5,6-dimethylbenzo-1,3-imidazolium(H3) chloride

• An unusual anhydrous dimethylbenzo-1,3-imidazole chloride salt was prepared.
• Molecular structure was studied via XRD and DFT calculations (B3LYP/6-311++G∗∗ level).
• Evaluation of N–H⋯Cl− H-bond parameters at solid state and gas phase was performed.
• IR experimental and computed data nicely model N–H⋯Cl− interactions in bio-systems.

The heteroaromatic base 5,6-dimethylbenzo-1,3-imidazole (DMBI) proved to be a Brönsted base in an anhydrous ethanol solution, which contained fac,trans-[Ru(CO)3Cl2]2 at 55 °C in air when the DMBI:Ru molar ratio was 2:1. The reaction produced colorless anhydrous single crystals of {(HDMBI)+Cl−}, C9H11ClN2, which were collected and analyzed using X-ray diffraction (XRD) techniques. A network of N–H⋯Cl hydrogen bond type interactions linking the protonated hetero-aromatic base to the chloride anions (bridging bases) stabilizes the crystal and mimics the N–H⋯Cl− interactions that play important roles in CCl channel biological systems. The shortest N⋯Cl contact distance and corresponding N–H⋯Cl angle are 3.073(3) Å and 173(3)°, respectively. The packing is also assisted by weaker C–H⋯Cl− hydrogen bond-type interactions and an extensive network of π⋯π stacking interactions involving HDMBI+ cations. Density functional calculations at the B3LYP/6-31G∗∗ and /6-311++G∗∗ levels for models of fragments of the crystal structure allowed for the evaluation of geometric parameters, hydrogen bond-type interaction formation energies, and infrared parameters for {(HDMBI)+Cl−} and {(HDMBI)+⋯Cl−⋯(HDMBI)+}.

Anhydrous chloride salt {(HDMBI)+Cl−} was isolated by reaction of fac,trans-[Ru(CO)3Cl2]2 and DMBI (5,6-dimethylbenzo-1,3-imidazole; ratio 2:1, Ru:ligand) in absolute ethanol. The crystal structure packing showed a network of N–H⋯Cl, C–H⋯Cl and π⋯π interactions.Figure optionsDownload as PowerPoint slide