Comparative study of the gas-phase bond strengths of CO 2 and N 2O with the halide ions

Abstract

Thermodynamic data, δ H° n−1,n and δ S° −1, n, for clustering reactions of halide ions X − (X = F, Cl, Br, and I) with N 2O were measured with a pulsed electron beam high-pressure mass spectrometer. In contrast to the fact that CO 2 forms a covalent bond with the fluoride ion to yield the fluoroformate ion, FCO − 2, the interaction between F − and N 2O is mainly electrostatic. It was found that the cluster ions F − (N 2O) n complete the first shell at n = 6, thus forming an octahedral structure. The difference between F—CO − 2 and F − ⋯ N 2O is discussed in terms of Coulombic, exchange, and charge-transfer interactions. The X − (N 2O) 2 clusters (X = Cl, Br and I) are found to be of C 2h symmetry, while F − (N 2O) 2 is of a twisted form and is slightly asymmetric due to a slight participation of covalency (charge transfer) in the core ion F − ··· N 2O.