Structures of the (Imidazole)nH+ ... Ar (n=1,2,3) complexes determined from IR spectroscopy and quantum chemical calculations

Abstract

Here, we present new cryogenic infrared spectra of the (Imidazole)$$_{n}\mathrm{H}^{+}$$ n H + (n=1,2,3) ions. The data was obtained using helium tagging infrared predissociation spectroscopy. The new results were compared with the data obtained by Gerardi et al. (Chem. Phys. Lett. 501:172–178, 2011) using the same technique but with argon as a tag. Comparison of the two experiments, assisted by theoretical calculations, allowed us to evaluate the preferable attachment positions of argon to the (Imidazole)$$_{n}\mathrm{H}^{+}$$ n H + frame. Argon attaches to nitrogen-bonded hydrogen in the case of the (Imidazole)H$$^+$$ + ion, while in (Imidazole)$$_{2}\mathrm{H}^{+}$$ 2 H + and (Imidazole)$$_{3}\mathrm{H}^{+}$$ 3 H + the preferred docking sites for the argon are in the center of the complex. This conclusion is supported by analyzing the spectral features attributed to the N–H stretching vibrations. Symmetry adapted perturbation theory (SAPT) analysis of the non-covalent forces between argon and the (Imidazole)$$_{n}\mathrm{H}^{+}$$ n H + (n=1,2,3) frame revealed that this switch of docking preference with increasing complex size is caused by an interplay between induction and dispersion interactions.

Electronic Fingerprint of the Protonated Imidazole Dimer Probed by X-ray Absorption Spectroscopy

“…In contrast, the geometrically relaxed saddle point, where the shared proton is in the middle of the dimer, yields a much reduced barrier height of 0.04 eV (i.e., well below the ZPE). The latter finding coincides qualitatively with earlier gas-phase studies − and, with its more delocalized description of the shared proton, is in line with the experimentally observed broad Zundel-like IR absorption bands. Since the rigid scans are restricted to changing only one parameter, the N–H distance, it is important to point out the intrinsic multidimensionality of the system: additional degrees of freedom of the imidazole moieties as well as fluctuations in the solvation shell are known to influence the potential energy landscape, experienced by the shared proton, and thus would require the sampling of a whole range of structures via AIMD simulations.…”

Cobalt–Imidazole Complexes: Effect of Anion Nature on Thermochemical Properties

“…However, the absorption bands of the N-H stretching vibrations are shifted to a higher-frequency region (from 3100 to 3300 cm −1 ). As was demonstrated in [ 21 , 22 ] based on calculation methods, such changes can be explained by the breaking of hydrogen bonds between imidazole molecules. The reason of their formation is the presence of a weakly acidic >N-H group in the imidazole ring and a nitrogen atom (–N=) with a lone electron pair capable of proton attaching.…”