Pre-reactive Complexes in Mixtures of Water Vapour with Halogens: Characterisation of H2O⋅⋅⋅ClF and H2O⋅⋅⋅F2 by a Combination of Rotational Spectroscopy and Ab initio Calculations

Abstract

Complexes H2O...ClF and H2O...F2 were detected by means of their ground-state rotational spectra in mixtures of water vapour with chlorine monofluoride and difluorine, respectively. A fast-mixing nozzle was used in conjunction with a pulsed-jet, Fourier-transform microwave spectrometer to preclude the vigorous chemical reaction that these dihalogen species undergo with water. The ground-state spectra of seven isotopomers (H2 16O...35ClF, H2 16O...ClF, H2 18O...35ClF, D2 16O... 35ClF, D2 16O...37ClF, HDO...35ClF and HDO...37ClF) of the ClF complex and five isotopomers (H2O...F2, H2 18O...F2, D2O...F2, D2 18O...Fi and HDO...F2) of the F2 complex were analysed to yield rotational constants, quartic centrifugal distortion constants and nuclear hyperfine coupling constants. These spectroscopic constants were interpreted with the aid of simple models of the complexes to give effective geometries and intermolecular stretching force constants. Isotopic substitution showed that in each complex the H2O molecule acts as the electron donor and either CIF or F2 acts as the electron acceptor, with nuclei in the order H2O...ClF or H2O...F2. For H2O...ClF, the angle phi between the bisector of the HOH angle and the O...Cl internuclear line has the value 58.9(16)degrees, while the distance r(O...Cl)= 2.6081(23) A. The corresponding quantities for H2O...F2 are phi = 48.5(21)degrees and r(O...Fi) = 2.7480(27) A, where Fi indicates the inner F atom. The potential energy V(phi) as a function of the angle phi was obtained from ab initio calculations at the aug-cc-pVDZ/MP2 level of theory for each complex by carrying out geometry optimisations at fixed values of phi in the range +/-80degrees. The global minimum corresponded to a complex of Cs symmetry with a pyramidal configuration at O in each. The function V(phi) was of the double-minimum type in each case with equilibrium values phie = +/-55.8degrees and +/-40.5degrees for H2O...ClF and H2O...F2, respectively. The barrier at the planar C2v conformation was V0= 174cm(-1) for H2O...ClF and 7cm(-1) for H2O...F2. For the latter complex, the zero-point energy level lies above the top of the barrier.

Monohydrate of argentous fluoride: H2O⋯AgF characterised by rotational spectroscopy and ab initio calculations

“…The rotational spectrum of H 2 OÁ Á ÁAg-F so generated was recorded with a pulsed-jet, Fourier transform microwave spectrometer and the spectroscopic constants obtained from spectral analysis were interpreted to give the geometry and one measure of the interaction strength of the two molecules forming this novel compound. These properties are compared here with those generated ab initio at the CCSD(T)/ccpVQZ level of theory and with those obtained experimentally for the hydrogen-and halogen-bonded complexes H 2 OÁ Á ÁHF, H 2 OÁ Á ÁF 2 and H 2 OÁ Á ÁClF [12][13][14].…”

“…The determined r 0 value of / is 41.9(11)°. This angle is similar in magnitude to those measured for H 2 OÁ Á ÁHF, H 2 OÁ Á ÁF 2 and H 2 OÁ Á ÁClF [12][13][14]. Angle / degrees Fig.…”

The Interaction of Water and Dibromine in the Gas Phase: An Investigation of the Complex H2O⋅⋅⋅Br2 by Rotational Spectroscopy and Ab Initio Calculations

“…A similar approach to that described in the preceding paragraph has now been applied to six complexes of the type H 2 O ¥¥¥ XY, namely those in which XY is F 2 , [6,7] Cl 2 , [9] Br 2 , BrCl, [10] ClF [7,8] and ICl. [11] It is timely to compare the properties of the complexes determined in this way.…”

“…Finally, we note the result that all complexes, even H 2 O ¥¥¥ F 2 , [7] have a pyramidal configuration at O and C s symmetry at the equilibrium geometry. This makes it clear that all of these complexes obey the rule originally put forward to account for the observed geometries of hydrogenbonded complexes B ¥¥¥ HX [44,45] and recently extended [4,5] to include complexes B ¥¥¥ XY involving dihalogen molecules.…”

“…So far, comparisons of the properties of the two series for a range of Lewis bases B have revealed a parallelism that suggests it is appropriate to describe this interaction B ¥¥¥ XY as a halogen bond. In the specific series H 2 O ¥¥¥ XY, the examples where XY is F 2 , [6,7] ClF, [7,8] Cl 2 , [9] BrCl [10] and ICl [11] have already been examined by our combined experimental/computational approach. The present results for H 2 How does this vary with atom X and how does it vary when X is held constant and Y is changed?…”