Structure and Bonding of Chlorine Oxides and Peroxides: ClO<i>_x</i>, ClO<i>_x</i>^-(<i>x</i>= 1−4), and Cl₂O<i>_x</i>(<i>x</i>= 1−8)

Abstract

The structural and bonding properties of the chlorine oxides and peroxides ClOx, ClOx-, (x = 1−4) and Cl2Ox (x = 1−8) in their ground state have been investigated with the hybrid spin unrestricted and spin restricted Hartree−Fock density functional method. The equilibrium structures of the most stable isomers in each stoichiometry have been determined. It is found that the di-chlorine oxides avoid the formation of a Cl−Cl bond, and therefore have either an oxo or peroxo structure. The calculated vibrational harmonic frequencies are in good agreement with the available gas phase or matrix isolation IR data. The calculated adiabatic electron affinities of the mono-chlorine species are, respectively, 2.23, 2.14, 4.07, and 5.1 eV for ClO, ClO2, ClO3, and ClO4. The reaction enthalpies of the possible channels leading to the formation of di-chlorine oxides and peroxides Cl2Ox from mono-chlorine oxide fragments are reported and discussed. A comparative discussion of the bonding in these species has been carried out on the basis of the topological analysis of the electron localization function (ELF). It is found that the odd electron of the mono-chlorine species is distributed on the oxygen and chlorine lone pairs. The weak populations of the ClO bond basins and the absence of spin density within them leads to discarding a picture in which three electrons are involved in the ClO bond. The localization of the spin density in the mono-chlorine oxides determines the reactive center: oxygen for ClO and ClO4, chlorine for ClO2 and ClO3. The formation of the di-chlorine oxides and peroxides from the mono-chlorinated species follows the two following rules: (i) the formation of a Cl−Cl bond never yields the most stable isomer, (ii) the chemical bond linking the two fragments is formed between their reactive centers provided rule (i) is satisfied.