Vibrations of a chelated proton in a protonated tertiary diamine

TitleVibrations of a chelated proton in a protonated tertiary diamine
Publication TypeJournal Article
Year of Publication2011
AuthorsG.JO Beran, E.L Chronister, L.L Daemen, A.R Moehlig, L.J Mueller, J. Oomens, A. Rice, D.R Santiago-Dieppa, F.S Tham, K. Theel, S. Yaghmaei, T.H Morton
JournalPhysical Chemistry Chemical Physics
Volume13
Issue45
Number45
Pagination20380-20392
Type of ArticleArticle
ISBN Number1463-9076
KeywordsBASIS-SETS, dissociation, DOUBLE-MINIMUM POTENTIALS, ENERGY SURFACES, GAS-PHASE, INFRARED-SPECTROSCOPY, PREDISSOCIATION SPECTRA, SHORT HYDROGEN-BOND, SOLID-STATE, STATE N-15 NMR
Abstract

Vibrational spectra of the conjugate acid of Me(2)NCH(2)CH(2)CH(2)CH(2)NMe(2) (N,N,N',N'-tetramethylputrescine) have been examined in the gaseous and crystalline phases using Infrared Multiple Photon Dissociation (IRMPD) spectroscopy, Inelastic Neutron Scattering (INS), and high pressure Raman spectroscopy. A band observed near 530 cm(-1) is assigned to the asymmetric stretch of the bridging proton between the two nitrogens, based on deuterium substitution and pressure dependence. The NN distance measured by X-ray crystallography gives a good match to DFT calculations, and the experimental band position agrees with the value predicted from theory using a 2-dimensional potential energy surface. The reduced dimensionality potential energy surface, which treats the ion as though it possesses a linear NHN geometry, shows low barriers to proton transit from one nitrogen to the other, with zero point levels close to the barrier tops. In contrast, two other related systems containing strong hydrogen bonds do not exhibit the same spectroscopic signature of a low barrier hydrogen bond (LBHB). On the one hand, the IRMPD spectra of the conjugate acid ions of the amino acid N,N,N',N'-tetramethylornithine (in which the two nitrogens have different basicities) show fewer bands and no comparable isotopic shifts in the low frequency domain. On the other hand, the IRMPD spectrum of the shorter homologue Me(2)NCH(2)CH(2)CH(2)NMe(2) (N,N,N',N'-tetramethyl-1,3-propanediamine), for which the NHN bond angle deviates substantially from linearity, displays more than one band in the 1100-1400 cm(-1) domain, which vanish as a consequence of deuteration.

DOI10.1039/c1cp22065a
Division

GUTHz

Department

Moldyn

PID

4214ce3b97422baee33be28e9a9acc44

Alternate TitlePhys. Chem. Chem. Phys.

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