Complex hydrogen bonded cations. The imdazole/imidazolium complex cation

Abstract

The salts (ImH + )X − , Im = imidazole, X − = PF 6 − , BF 4 − , or ClO 4 − have been prepared in solution, and the perchlorate salt has been crystallised. The molecularity implied by the formula is confirmed in solution by Job's method, and for the crystals gravimetrically. In MeCN the association constant is ∼8 M −1 . Infrared spectra of solution and crystals are similar, independent of counter ion, and indicate an asymmetric single minimum proton potential. The pronounced doublet in the NH stretching band of the H bridged complex, and replaced by a single band in the D bridged analogue, is not indicative of proton tunnelling. The X-ray structure is compatible with this interpretation of the spectra.