Closing the Shell: Gas-Phase Solvation of Halides by 1,3-Butadiene.

Gas-phase solvation of halides by 1,3-butadiene has been studied via a combination of photoelectron spectroscopy and density functional theory. Photoelectron spectra for X- ⋯(C4 H6 )n (X=Cl, Br, I where n=1-3, 1-3 and 1-7 respectively) are presented. For all complexes, the calculated structures indicate that butadiene is bound in a bidentate fashion through hydrogen-bonding, with the chloride complex showing the greatest degree of stabilisation of the internal C-C rotation of cis-butadiene. In both Cl- and Br- complexes, the first solvation shell is shown to be at least n = 4 ${n = 4}$ from the vertical detachment energies (VDEs), however for I- , increases in the VDE may suggest a metastable, partially filled, first solvation shell for n = 4 ${n = 4}$ and a complete shell at n = 6 ${n = 6}$ . These results have implications for gas-phase clustering in atmospheric and extraterrestrial environments.

Hydrogen Bonding versus Halogen Bonding: Spectroscopic Investigation of Gas-Phase Complexes Involving Bromide and Chloromethanes.

Hydrogen bonding and halogen bonding are important non-covalent interactions that are known to occur in large molecular systems, such as in proteins and crystal structures. Although these interactions are important on a large scale, studying hydrogen and halogen bonding in small, gas-phase chemical species allows for the binding strengths to be determined and compared at a fundamental level. In this study, anion photoelectron spectra are presented for the gas-phase complexes involving bromide and the four chloromethanes, CH3 Cl, CH2 Cl2 , CHCl3 , and CCl4 . The stabilisation energy and electron binding energy associated with each complex are determined experimentally, and the spectra are rationalised by high-level CCSD(T) calculations to determine the non-covalent interactions binding the complexes. These calculations involve nucleophilic bromide and electrophilic bromine interactions with chloromethanes, where the binding motifs, dissociation energies and vertical detachment energies are compared in terms of hydrogen bonding and halogen bonding.

A tale of two conformers: spectroscopic evidence for halide catalysed formic acid isomerisation.

Halide-formic acid complexes have been studied utilising a combined experimental and theoretical approach. Formic acid exists as two conformers, distinguished by the relative rotation about the C-OH bond. Computational investigation of the formic acid isomerisation reaction between the two conformers has revealed the ability of halide anions to catalyse the formation of, and preferentially stabilise, the higher energy conformer. Anion photoelectron spectroscopy has been used to study the halide-formic acid complexes, with the experimental vertical detachment energies compared with simulated photodetachment energies with respect to halide complexes with both formic acid conformers. The existence of experimental spectral features associated with halide complexes of the higher energy formic acid confomer confirms in situ generation, likely as a result of the halide mediated catalytic formation.

Spectroscopic Study of the Br- +CH3 I→I- +CH3 Br SN 2 Reaction.

Mass spectrometry and anion photoelectron spectroscopy have been used to study the gas-phase S N 2 ${{{\rm S}}_{{\rm N}}2}$ reaction involving B r - ${{{\rm B}{\rm r}}^{-}}$ and C H 3 I ${{{\rm C}{\rm H}}_{3}{\rm I}}$ . The anion photoelectron spectra associated with the reaction intermediates of this S N 2 ${{{\rm S}}_{{\rm N}}2}$ reaction are presented. High-level CCSD(T) calculations have been utilised to investigate the reaction intermediates that may form as a result of the S N 2 ${{{\rm S}}_{{\rm N}}2}$ reaction along various different reaction pathways, including back-side attack and front-side attack. In addition, simulated vertical detachment energies of each reaction intermediate have been calculated to rationalise the photoelectron spectra.

Towards an Understanding of Halide Interactions with the Carbonyl-Containing Molecule CH3 CHO.

The anion photoelectron spectra of Cl- ⋅⋅⋅CD3 CDO, Cl- ⋅⋅⋅(CD3 CDO)2 , Br- ⋅⋅⋅CH3 CHO, and I- ⋅⋅⋅CH3 CHO are presented with electron stabilisation energies of 0.55, 0.93, 0.48, and 0.40 eV, respectively. Optimised geometries of the singly solvated species featured the halide appended to the CH3 CHO molecule in-line with the electropositive portion of the C=O bond and having binding energies between 45 and 52 kJ mol-1 . The doubly solvated Cl- ⋅⋅⋅(CH3 CHO)2 species features asymmetric solvation upon the addition of a second CH3 CHO molecule. Theoretical detachment energies were found to be in excellent agreement with experiment, with comparisons drawn between other halide complexes with simple carbonyl molecules.

Spectroscopic Investigation of Chalcogen Bonding: Halide-Carbon Disulfide Complexes.

A combined experimental and theoretical approach has been used to study intermolecular chalcogen bonding. Specifically, the chalcogen bonding occurring between halide anions and CS2 molecules has been investigated using both anion photoelectron spectroscopy and high-level CCSD(T) calculations. The relative strength of the chalcogen bond has been determined computationally using the complex dissociation energies as well as experimentally using the electron stabilisation energies. The anion complexes featured dissociation energies on the order of 47 kJ/mol to 37 kJ/mol, decreasing with increasing halide size. Additionally, the corresponding neutral complexes have been examined computationally, and show three loosely-bound structural motifs and a molecular radical.