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....

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Veröffentlicht in:The Journal of chemical physics 2004-05, Vol.120 (18), p.8645-8650
Hauptverfasser: Lee, Kwang Ming, Chang, Hai-Chou, Jiang, Jyh-Chiang, Lu, Li-Chuan, Hsiao, Chia-Jung, Lee, Yi-Ting, Lin, Sheng Hsien, Lin, Ivan J. B.
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Sprache:eng
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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