Bis(benzimidazolium)methane salts: a potential guest for dibenzo-24-crown-8 towards [2]pseudorotaxanes

We investigated the threading of bis(benzimidazolium) methane moieties with DB24C8 at 35 °C (room temperature) and found a high degree of association. The presence of threaded complexes was determined by 1H NMR and also supported by high resolution mass spectrometry and B3LYP/6-31G**++calculations. A 2D NMR study was done to elucidate the host–guest geometry and the molecular interactions present. The variable temperature NMR experiment was done over a temperature range of 243–323 K. The threading was stable and visible even at 323 K. Acid–base equilibrium established the reversibility of the process. DFT optimized structures establish that two H-bonded links are present between O1⋯O4′ and O3⋯O2′ across the dibenzo axis of the crown.