CMM-RS Potential for Characterization of the Properties of the Halogen-Bonded OC–Cl₂ Complex, and a Comparison with Hydrogen-Bonded OC–HCl

Abstract

Transitions associated with the vibrations ν₁, ν₁ + ν(b)¹, ν₁ + ν₅¹, and ν₁ + ν₅¹ - ν₅¹ of the complex OC···Cl₂ have been rovibrationally analyzed for several isotopologues involving isotopic substitutions in Cl₂. Spectra were recorded using a recently constructed near-infrared (4.34 to 4.56 μm), quantum-cascade laser spectrometer with cw supersonic slit jet expansion. Spectral analysis allowed precise determination of the ν₅¹ intermolecular vibration of OC-³⁵Cl₂ to be 25.977637(80) cm⁻¹. These results were incorporated with other previously determined data into a spectroscopic database for generation of a five-dimensional morphed potential energy surface. This compound-model morphed potential with radial shifting (CMM-RS) was then used to make more accurate predictions of properties of the OC-³⁵Cl₂ complex including D(e) = 544(5) cm⁻¹, D₀ = 397(5) cm⁻¹, ν₃ = 56.43(4) cm⁻¹, and ν(b)¹ = 85.43(4) cm⁻¹. The CMM-RS potential determined for OC-Cl₂ was also used to compare quantitatively many of the inherent properties of this non-covalent halogen bonded complex with those of the closely related hydrogen-bonded complex OC-HCl, which has a similar dissociation energy D₀. We found that in the ground state, the CO bending amplitude is larger in OC-Cl₂ than in OC-HCl.

A reduced radial potential energy function for the halogen bond and the hydrogen bond in complexes B⋯XY and B⋯HX, where X and Y are halogen atoms

“…The quantities o s and o s x s have proved difficult to obtain experimentally, but Bevan, Lucchese and co-workers [93][94][95] 3), thereby providing some confidence in the approximations alluded to. This confidence is reinforced by the similar quality of agreement found between the values k s = 3.668(3), 3.751(5) and 4.5(4) implied by the o s from morphed potential energy functions 94,95…”

A comparative view on the potential acting on an electron in a molecule and the electrostatic potential through the typical halogen bonds

“…The potential accounting for the exchange and correlation of electrons makes the barriers of halogen bonds noticeably lower in comparison with the ESP. Comparison of values with the stretching force constants of the halogen bonds, k σ , estimated by Legon et al, shows that the more lower barriers correspond to the more stronger halogen bonds (Figure S1 in Supporting Information). In complexes of the strong electron donor, NH 3 , for relatively stronger halogen bonds, the and barriers are lower than in complexes with the weakest electron donor CO.…”

The Halogen Bond

“…As an example, J. W. Bevan and co-workers have recently shown high-resolution vibration–rotation spectroscopic studies on Cl 2 ···CO complexes using quantum cascade lasers. 282 …”