FORMATION OF THE CHELATE BONDS IN THE CLUSTER O2-(CO2)N, CO3-(CO2)N, AND NO2-(CO2)N

The equilibria of gas-phase clustering reactions of O2-, CO3-, and NO2- with CO2 were studied with a pulsed electron beam high-pressure mass spectrometer. Thermochemical stabilities of the clusters O2-(CO2)n, CO3-(CO2)n, and NO2-(CO2)n with n = 1-8 were determined. For O2-(CO2)n, irregular decreases in the values of - DELTA-H(n-1,n)0 were observed between n = 1 and 2, and n = 3 and 4. These gaps indicate that the bond with covalent character is formed through the charge transfer (CT) O2- --> CO2 and the CT complex Of O2COO- accommodates two CO2 molecules preferably [i.e., O2COO- (CO2)2]. The - DELTA-H(n-1,n)0 values of both CO3-(CO2)n and NO2-(CO2)n clusters show an irregular decrease between n = 4 and 5. This suggests the formation of shells, OCO2-(CO2)4 and NO2-(CO2)4. Ab initio optimized geometries of these clusters are found to be composed of bridge (i.e., chelate) intermolecular bonds.