Gas-phase reactions of carbon dioxide with atomic transition-metal and main-group cations: Room-temperature kinetics and periodicities in reactivity

The chemistry of carbon dioxide has been surveyed systematically with 46 atomic cations at room temperature using an inductively-coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer. The atomic cations were produced at ca. 5500 K in an ICP source and allowed to cool radiatively and to thermalize by collisions with Ar and He atoms prior to reaction downstream in a flow tube in helium buffer gas at 0.35 +/- 0.01 Torr and 295 +/- 2 K. Rate coefficients and products were measured for the reactions of first-row atomic ions from K+ to Se+, of second-row atomic ions from Rb+ to Te+ (excluding Tc+), and of third-row atomic ions from Cs+ to Bi+. CO2 was found to react in a bimolecular fashion by 0 atom transfer only with 9 early transition-metal cations: the group 3 cations Sc+, Y+, and La+, the group 4 cations Ti+, Zr+, and Hf+, the group 5 cations Nb+ and Ta+, and the group 6 cation W+. Electron spin conservation was observed to control the kinetics of 0 atom transfer. Addition of CO2 was observed for the remaining 37 cations. While the rate of addition was not measurable some insight was obtained into the standard free energy change, Delta G degrees, for CO2 ligation from equilibrium constant measurements. A periodic variation in Delta G degrees was observed for first row cations that is consistent with previous calculations of bond energies D-0(M+-CO2). The observed trends in D-0 and Delta G degrees are expected from the variation in electrostatic attraction between M+ and CO2 which follows the trend in atomic-ion size and the trend in repulsion between the orbitals of the atomic cations and the occupied orbitals of CO2. Higher-order CO2 cluster ions with up to four CO2 ligands also were observed for 24 of the atomic cations while MO2+ dioxide formation by sequential O atom transfer was seen only with Hf+, Nb+, Ta+, and W+.