Ig. Shenderovich et al., NUCLEAR-MAGNETIC-RESONANCE OF HYDROGEN-BONDED CLUSTERS BETWEEN F- AND(HF)(N) - EXPERIMENT AND THEORY, Berichte der Bunsengesellschaft fur Physikalische Chemie, 102(3), 1998, pp. 422-428
Citations number
51
Categorie Soggetti
Chemistry Physical
Journal title
Berichte der Bunsengesellschaft fur Physikalische Chemie
Liquid state H-1 and F-19 NMR experiments in the temperature range bet
ween 110 and 150 K have been performed on mixtures of tetrabutylammoni
um fluoride with HF dissolved in a 1:2 mixture of CDF3 and CDF2Cl. Und
er these conditions hydrogen bonded complexes between F- and a varying
number of HF molecules were observed in the slow proton and hydrogen
bond exchange regime. At low HF concentrations the well known hydrogen
bifluoride ion [FHF](-) is observed, exhibiting a strong symmetric H-
bond. At higher HF concentrations the species [F(HF)(2)](-), [F(HF)(3)
](-) are formed and a species to which we assign the structure [F(HF)(
4)](-). The spectra indicate a central fluoride anion which forms mult
iple hydrogen bonds to HE With increasing number of HF units the hydro
gen bond protons shift towards the terminal fluorine's. The optimized
gas-phase geometries of [F(HF)(n)](-), n=1 to 4, calculated using ab i
nitio methods confirm the D-infinity h, C-2v, D-3h and T-d symmetries
of these ions. For the first time, both one-bond couplings between a h
ydrogen bond proton and the two heavy atoms of a hydrogen bridge, here
(1)J(HF) and (1)J(HF'), where \(1)J(HF)\greater than or equal to\(1)J
(HF')\, as well as a a two-bond coupling between the heavy atoms, here
(2)J(FF), have been observed. The analysis of the differential width
of various multiplet components gives evidence for the signs of these
constants, i.e. (1)J(HF) and (2)J(SF)>0, and (1)J(HF')<0. Ab initio ca
lculations of NMR chemical shifts and the scalar coupling constants us
ing the Density Functional formalism and the Multiconfiguration Comple
te Active Space method show a reasonable agreement with the experiment
al parameters and confirm the covalent character of the hydrogen bonds
studied.