On the nature of blueshifting hydrogen bonds: Ab initio and density functional studies of several fluoroform complexes

Abstract

Hydrogen-bond assisted enormous broadening of infrared spectra of phenol-water cationic cluster: An ab initio mixed quantum-classical study Potential energy hypersurfaces ͑PESs͒ for four fluoroform complexes ͑with acetonitrile, ethyleneoxide, formaldehyde, and water͒ were explored at the HF, MP2, and B3LYP/6-311 ϩϩG(d,p) levels of theory. Anharmonic C-H stretching vibrational frequency shifts are reported for all minima located on the studied PESs. In all cases, the lowest-energy minimum occurs for a C-H¯O(N) hydrogen-bonded arrangement and is characterized by a significant C-H frequency blueshift ͑upshift͒, while additional minima ͓for ''reversed'' orientations, in which there is no direct C-H¯O(N) contact͔ show only small C-H frequency upshifts. The large blueshifts found for the hydrogen-bonded arrangements are predominantly caused by the electronic exchange interaction, as revealed by Kitaura-Morokuma ͑KM͒ analysis, while the purely electrostaticϩpolarization interaction leads to C-H frequency redshifts, which was proven both by the KM analysis and the charge field perturbational ͑CFP͒ approach. The large net blueshifting effect of the exchange contribution is only possible thanks to the smallness of the redshifting electrostaticϩpolarization contribution, which, in turn, is a consequence of the fact that d (0) /dr CH is negative for the fluoroform molecule. In all cases the charge transfer as well as the dispersion energy contributions lead to frequency redshifts. The small C-H blueshifts for the reversed orientations are almost completely governed by the electrostatic interaction, as shown by the KM and CFP analyses. All these characteristics of blueshifting H bonds are in line with a previously outlined general model concerning ''standard'' and ''blueshifting'' H-bonding interactions ͓K. Hermansson, J. Phys. Chem. A 106, 4695 ͑2002͔͒.

On Differences between Hydrogen Bonding and Improper Blue‐Shifting Hydrogen Bonding

“…On the one hand Hobza et al [8,12] suggested that it non-negligibly contributes to the blue shift in some blue-shifting complexes, on the other hand according to Pejov and Hermansson [13] the dispersion causes a small red shift. Because the conclusions of Pejov and Hermansson are based on the differences between HF and MP2 methods, which comprise of not only dispersion but also changes to the electrostatics and induction due to correlation, we believe that a more sophisticated method should be used to extract the dispersion contribution to the blue shift.…”

Theoretical Investigations into the Blue‐Shifting Hydrogen Bond in Benzene Complexes

“…The repulsion-wall model seems to be physically justified but was recently questioned by Pejov and Hermansson. [21] We decided in the present study to reinvestigate its applicability for complexes of benzene (CÀH proton donor) and various proton acceptors represented by benzene, antracene and ovalene. The main attractive force, the London dispersion force, is systematically increasing in the series studied.…”

Pair interaction energy decomposition analysis

“…2 Their energy decomposition approach (EDA, also called sometimes the KM analysis) has become standard [3][4][5] and has been widely used during the 30 years since its appearance. [6][7][8] It also served as a basis to a great number of further improvements and development. [9][10][11][12][13] The original method applied to the analysis of binding between two units (e.g., molecules), and it was extended into a general case of an arbitrary number of units by Chen and Gordon 14 (whose practical implementation was limited to at most 10 units).…”