How are CO molecules bound to NO+? Shell formation of the gas-phase cluster ions of NO+(CO)n with n=4 and 8

Thermochemical data for a gas-phase clustering reaction, NO+(CO)n−1+CO = NO+(CO)n, were measured with a pulsed electron-beam high-pressure mass spectrometer. The thermochemical values, −ΔHn−1, no and −ΔSn−1, no, with n=1–9 have been determined. The cluster ion was found to have the shell structure, NO+(CO)4(CO)4(CO)n−8. The stability and structure of the cluster ions were investigated by ab initio calculations. The first four and second four CO ligands were found to attack the N and O atoms of NO+, respectively, to form a C4v structure. The calculated bond energies of the cluster ions NO+(CO)n with n=1–4 are in excellent agreement with the experimental.