Experimental and Theoretical Characterization of a Lone Pair−π Complex: Water–Hexafluorobenzene

Abstract

The lone pair-π interaction between H(2)O and C(6)F(6) was studied using matrix isolation infrared spectroscopy and quantum chemical calculations. Co-deposition of H(2)O with C(6)F(6) in a nitrogen matrix at 17 K followed by annealing to 30 K, results in the appearance of multiple new peaks in the infrared spectrum that are shifted from the H(2)O and C(6)F(6) parent absorptions. These peaks only appear when both the H(2)O and C(6)F(6) are present and have been assigned to distinct structures of a 1:1 H(2)O·C(6)F(6) complex. Similar experiments were performed with D(2)O and HDO and the corresponding infrared peaks for the structures of the D(2)O·C(6)F(6) and HDO·C(6)F(6) complexes have also been observed. Theoretical calculations were performed for the H(2)O·C(6)F(6) complex using the B3LYP, MP2, and CCSD(T) methods. Geometry optimizations at the B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ levels of theory located three structural minima, all of which involve the lone pair-π interaction between the H(2)O and the C(6)F(6) ring, but with different relative orientations of the H(2)O and C(6)F(6) subunits. BSSE corrected interaction energies were estimated at the CCSD(T)/aug-cc-pVTZ level and found to be between -11.2 and -12.3 kJ/mol for the three H(2)O·C(6)F(6) structures. Vibrational frequencies for the each of the structures were calculated at the B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ levels. The frequencies calculated with both methods support the assignments of the observed new peaks in the infrared spectra to the structures of the H(2)O·C(6)F(6) complex; however, the B3LYP calculated frequency shifts were found to be in better quantitative agreement with the experimentally observed frequency shifts.

Lone pair···π interactions involving an aromatic π-system: Complexes of hexafluorobenzene with dimethyl ether and trimethylamine

“…Possible assignments are the double combination 11 + 19 , the triple combination 14 + 17 + 18 and the quadruple combinations 8 + 2 14 + 20 , 10 + 11 + 14 + 20 and 14 + 17 + 2 20 . It should also be noted that the relative intensity of the bands in this spectral region differs strongly with those observed previously in a solid N 2 matrix, where the band at 1016.9 cm −1 is not observed [10], and the low resolution gas phase spectra, in which the band with the highest frequency has the largest intensity [39]. The infrared spectrum of the 12 and 13 spectral region of C 6 F 6 for a C 6 F 6 solution in LKr is given in Figure S3.…”

“…To aid the assignment of the DME-d 6 modes, the anharmonic force field of DME-d 6 was also calculated using Gaussian09 at the MP2/aug-cc-pVDZ level. For the assignment of C 6 F 6 , gas phase [38,39] and matrix isolation frequencies [10] found in the literature were used.…”

“…The most studied lp··· complex is undoubtedly the hexafluorobenzene-water (C 6 F 6 -H 2 O) complex, which has been described in much detail both theoretically [7,8] and experimentally [9][10][11][12][13]. The interest in C 6 F 6 can be attributed to its use as a solvent in several spectroscopic techniques as well as its use as a standard in 19 F NMR and 13 C NMR.…”

A molecular dynamics study of the evolution from the formation of the $${\text {C}}_{6}{\text {F}}_{6}$$ C 6 F 6 –( $${\text {H}}_{2}{\text {O}})_{n}$$ H 2 O ) n small aggregates to the $${\text {C}}_{6}{\text {F}}_{6}$$ C 6 F 6 solvation

“…The value of −11.25 kJ mol −1 obtained here for structure (a) is in the range of energies calculated by Gallivan et al, while the value of R O-C 6 F 6 = 2.9 Å corresponds to the lower limit of the distances interval. The same value of 2.9 Å has been given by Amicangelo et al [64] who reported BSSE-corrected energies estimated at the CCSD(T)/aug-cc-pVTZ level of calculation of −11.9 kJ mol −1 for an structure equivalent to the (a) one. On the other hand, matrix isolation infrared spectroscopy [64] provided experimental evidence of the most stable lone pair-π geometries in the C 6 F 6 -H 2 O complex, being the peaks on the spectrum assigned to structures in which H 2 O is placed above the aromatic plane.…”

Observation of exclusively π-stacked heterodimer of indole and hexafluorobenzene in the gas phase

“…This kind of π -hydrogen bond inhibition by fluorine substitution of the phenyl ring has also been reported in HFB · · · H 2 O complex, where a new non-covalent interaction namely n → π * is switched on. [48][49][50] The current work mainly focuses on the molecular level understanding on the nature and strength of the π -stacking interaction between indole and hexafluorobenzene. This knowledge, in particular, can help in designing synthetic proteins having specific aromatic-aromatic interaction between tryptophan and phenylalanine residues.…”