Formation of the chelate bonds in the cluster O−2(CO2)<i>n</i>, CO−3(CO2)<i>n</i>, and NO−2(CO2)<i>n</i>

The equilibria of gas-phase clustering reactions of O−2, CO−3, and NO−2 with CO2 were studied with a pulsed electron beam high-pressure mass spectrometer. Thermochemical stabilities of the clusters O−2(CO2)n, CO−3(CO2)n, and NO−2(CO2)n with n=1–8 were determined. For O−2(CO2)n, irregular decreases in the values of −ΔH0n−1,n 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) O−2→CO2 and the CT complex of O2COO− accommodates two CO2 molecules preferably [i.e., O2COO−(CO2)2]. The −ΔH0n−1,n values of both CO−3(CO2)n and NO−2(CO2)n clusters show an irregular decrease between n=4 and 5. This suggests the formation of shells, OCO−2(CO2)4 and NO−2(CO2)4. Ab initio optimized geometries of these clusters are found to be composed of bridge (i.e., chelate) intermolecular bonds.

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