Thermochemistry of the higher chlorine oxides ClO x ( x=3, 4) and Cl 2O x ( x=3–7)†

Abstract

Heats of formation for ClO 3, ClO 4, Cl 2O 3, Cl 2O 4, Cl 2O 5, Cl 2O 6 and Cl 2O 7 molecules are determined at the B3LYP, B3PW91, mPW1PW91 and B1LYP levels of the density functional theory employing a series of extended basis sets, and using Gaussian-3 model chemistries. Modified Gaussian-3 calculations, which employ accurate B3LYP/6-311+G(3d2f) molecular geometries and vibrational frequencies, were also performed. Heats of formation were calculated from both total atomization energies and isodesmic reaction schemes. The latter method in conjunction with Gaussian-3 models leads to the most reliable results. The best values at 298 K for ClO 3, ClO 4, Cl 2O 3 and Cl 2O 4 as derived from an average of G3//B3LYP and G3//B3LYP/6-311+G(3d2f) calculations are 43.1, 54.8, 31.7 and 37.4 kcal mol −1. From calculations carried out at the G3(MP2)//B3LYP and G3(MP2)//B3LYP/6-311+G(3d2f) levels, heats of formation for Cl 2O 5, Cl 2O 6 and Cl 2O 7 are predicted to be 53.2, 52.2 and 61.5 kcal mol −1. All best values are reproduced within 1 kcal mol −1 by using mPW1PW91/6-311+G(3d2f) isodesmic energies. Enthalpy changes for relevant Cl–O bond fission reactions are reported. Comparisons with previous thermodynamics data are made.