Cl − – C 6 H 6 ,  Br−–C6H6, and I−–C6H6 anion complexes: Infrared spectra and ab initio calculations

Abstract

Vibrational predissociation spectroscopy is used to obtain infrared spectra of the Cl−–C6H6, Br−–C6H6, and I−–C6H6 complexes in the region of the benzene CH stretch vibrations (2800–3200 cm−1). The infrared spectra of the three dimers are similar, each exhibiting several narrow bands (full width at half maximum <10 cm−1) that are only slightly redshifted from the absorptions of the free benzene molecule. Ab initio calculations predict that the most stable form of the three complexes is a planar C2v structure in which the halide is hydrogen bonded to two adjacent CH groups. The planar C2v structure in which the halide is linearly H bonded to a single CH group is predicted to be slightly less stable than the bifurcated form. Comparisons between experimental and theoretically predicted infrared spectra confirm that the bifurcated structure is indeed the most stable conformer for all three complexes. Ab initio calculations show that the electron density transfer from the halide to the benzene is not limited to the σ*(CH) orbitals adjacent to the halide, but extends to the σ domain of the benzene ring, consistent with the moderate shift of the CH stretch frequencies. The presence of weak satellite bands is explained in terms of Fermi resonances reminiscent of the benzene Fermi tetrad or hot bands involving the in-plane intermolecular bend vibration.

Infrared studies of ionic clusters: The influence of Yuan T. Lee

“…Additional peaks were shifted to lower frequency by ϳ12 cm −1 . 216 Studies of binary and larger clusters have also been conducted involving methane, 72,217 benzene, 218 and ethylene, 73 demonstrating continued growth in this area. Solvation by multiple methanols was considered, but from a slightly different perspective.…”

Benzene‐, Pyrrole‐, and Furan‐Containing Diametrically Strapped Calix[4]pyrroles—An Experimental and Theoretical Study of Hydrogen‐Bonding Effects in Chloride Anion Recognition

“…Such interactions, which involve both aliphatic and aryl C À H groups, have been inferred from gas-phase studies, [3] deduced from NMR spectroscopic studies through, for example, chemical-shift changes, [4][5][6][7] and observed in solidstate structures. [10,11] For instance, Hay and Bryantsev have calculated that benzene CÀH···anion hydrogen bonds are significant, [11a] being roughly half the strength of typical neutral NÀ H···anion hydrogen bonds. [9] These experimental observations are supported by theoretical analyses.…”

Infrared spectra of HC2−∙(C2H2)n and O2−∙(C2H2)n clusters (n=2–5)

“…Figure 3 shows the infrared spectra of HC 2 − · ͑C 2 H 2 ͒ n ͑n =2-5͒. Based on the results of Bieske and co-workers on halide-acetylene clusters, 23,24 we can immediately assign the intense absorption bands ͑1͒ and ͑2͒ to CH oscillators in ionic H bonds of the acetylene ligands to the ion. The spectra are dominated by two broad and intense absorptions around 2800-3000 cm −1 ͑denoted 1 and 2 in Fig.…”