Probing C–H⋯X hydrogen bonds in amide-functionalized imidazolium salts under high pressure
We have probed under high pressure the C–H hydrogen bonds formed by N,N′-disubstituted imidazolium ions having PF6− and Br− counterions. High-pressure infrared spectral profiles, x-ray crystallographic analysis, and ab initio calculations allow us to make a vibrational assignment of these compounds....
Gespeichert in:
Veröffentlicht in: | The Journal of chemical physics 2004-05, Vol.120 (18), p.8645-8650 |
---|---|
Hauptverfasser: | , , , , , , , |
Format: | Artikel |
Sprache: | eng |
Online-Zugang: | Volltext |
Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
Zusammenfassung: | We have probed under high pressure the C–H hydrogen bonds formed by N,N′-disubstituted imidazolium ions having PF6− and Br− counterions. High-pressure infrared spectral profiles, x-ray crystallographic analysis, and ab initio calculations allow us to make a vibrational assignment of these compounds. The appearance of a signal for the free-NH unit (or weakly bonded N–H⋯F unit) in the infrared spectrum of the PF6− salt indicates that conventional N–H⋯O and N–H⋯N hydrogen bonds do not fully dominate the packing. It is likely that the charge-enhanced C2–H⋯F interactions, combined with other weak hydrogen bonds, disturb the formation of N–H hydrogen bonds in the PF6− salt. This finding is consistent with the pressure-dependent results, which reveal that the C2–H⋯F interaction is enhanced upon increasing the pressure. In contrast to the PF6− salt, the imidazolium C–H bonds of the Br− salt have low sensitivity to high pressure. This finding suggests that the hydrogen bonding patterns are determined by the relative hydrogen bond acceptor strengths of the Br− and PF6− ions. |
---|---|
ISSN: | 0021-9606 1089-7690 |
DOI: | 10.1063/1.1697380 |