Infrared spectra are reported of strongly hydrogen-bonded complexes between ammonia or amines (methylamine, dimethylamine and trimethylamine) and hydrogen bromide trapped in argon and nitrogen matrices. There are substantial differences between the spectra of the complexes in the two matrices, which are attributed to increased proton transfer from hydrogen bromide to the amine in the more polar nitrogen matrix. The extent of proton transfer increases from ammonia-hydrogen bromide in an argon matrix (where the proton is shared more or less equally between the nitrogen and bromine atoms) to trimethylamine-hydrogen bromide in a nitrogen matrix (where the proton is almost completely transferred to the amine).Ault and Pimentel' reported i.r. spectra of a strongly hydrogen-bonded complex between ammonia and hydrogen chloride. Ault et a1. ' extended the study to other strongly hydrogen-bonded complexes including ammonia-hydrogen bromide, trimethylaminehydrogen chloride and trimethylamine-hydrogen bromide in nitrogen matrices. From a vibrational correlation diagram (a plot of relative HX frequency shift against normalised proton affinity difference) they deduced that the proton is more or less equally shared between the base and the halogen in the ammonia-hydrogen chloride complex while in the ammonia-hydrogen bromide complex and both trimethylamine complexes the proton is more closely associated with the base, i.e. the complexes are tending towards R3NH+X-.Detailed investigations of the i.r. spectra of the ammonia-hydrogen chloride complex3 and amine-hydrogen chloride complexes4 revealed striking differences between the spectra in argon and nitrogen matrices. These differences were attributed to an increase in the extent of proton transfer between argon and nitrogen matrices; the gas-phase complexes being expected to have an even lower degree of proton transfer than that found in argon matrices. It was thus concluded that for the amine-hydrogen chloride complexes, more or less equal sharing of the proton between the nitrogen and chlorine atoms probably occurs for dimethylamine in the gas phase (but for methylamine or ethylamine in an argon matrix and for ammonia in a nitrogen matrix). The present paper extends these studies to the corresponding hydrogen bromide complexes.
Infrared spectra are reported of strongly hydrogen-bonded complexes between dimethyl sulphoxide or [2H,]dimethyl sulphoxide and hydrogen chloride or hydrogen bromide in argon and nitrogen matrices. Although there are differences between the spectra of the complexes in the two matrices, the extent of proton transfer does not change markedly from an argon matrix to a nitrogen matrix (unlike the amine-hydrogen halide complexes). There is substantial mixing of the 0. -.H--C 1 stretching and bending modes with vibrational modes of the dimethyl sulphoxide molecule. In the hydrogen bromide complex, the proton is more or less equally shared between the oxygen and bromine atoms; the extent of proton transfer is smaller in the hydrogen chloride complex.
DMSO-Hydrogen Halide ComplexesTable 1. Bands observed (cm-') in i.r. spectra of DMSO in argon and nitrogen matrices ~~ ~~ mode description Ar matrix N2 matrix CH, asym. stretches (A', A") CH3 sym. stretches (A', A") 2v7 (A') CH3 asym. deformations ( A " ) CH, asym. deformation (A') CH3 asym. deformation ( A ' ) CH3 sym. deformation (A") CH3 sym. deformation (A') S=O stretch ( A ' ) dimer S=O stretch H 2 0 complex S=O stretch CH, rock (A') CH, rock (A") CH, rock ( A ' ) CH3 rock (A") C-S-C asym. stretch (A") C-S-C sym. stretch (A') C-S-0 sym. bend (A') C-S-0 asym. bend (A")
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