A theoretical study of (N 2O) 2+, (CO 2) 2+ and N 2O +CO 2. Comparison of the two-center—three-electron bond and the ion—dipole complex

Abstract

The binding energy of the (CO 2) 2 +, (N 2O) 2 + and N 2O +CO 2 complexes were calculated at the MP4/6-31G *//6-31G * and MP2/6-31+G * levels for two alternative structures. In one structure the positive charge is distributed evenly over both moieties, which leads to a two-center—three-electron (2c-3e) bonding interaction. In the other, one moiety carries the positive charge, which leads to an ion—dipole interaction. In the (CO 2) 2 + dimer the 2c-3e interaction is predicted to be 6 kcal mol −1 stronger than the ion—dipole interaction while in the (N 2O) 2 + dimer the 2c-3e interaction is 9 kcal mol −1 stronger. The binding energy of the (CO 2) 2 + dimer is in good agreement with experiment, but the binding energy of (N 2O) 2 + is overestimated by ≈6 kcal mol −1.