The thermochemical properties of gas-phase transition metal ion complexes

Gas phase ion clustering reactions of the form A+(L)n+L⇄A +(L)n+1 were studied using high pressure mass spectrometry. Equilibrium constants together with enthalpy, entropy, and free energy changes were determined for stepwise clustering reactions of water about the Ag+ ion with n=0 to5 and the Cu+ ion with n=2 to4, ammonia about the Ag+ and Cu+ ions from n=1 and n=2 to4, respectively, and pyridine about the Ag+ and H+ ion from n=2 and n=1 to 3, respectively. These results, together with those of other studies, show evidence for the existence of structure in some cluster ions. Considerations of bonding and entropy, together with comparisons with the results of ion chemistry in the liquid phase, suggest that such structures can be attributed to several types of cluster ion systems, including gas phase analogs of traditional ’’coordination complexes’’ known in the aqueous phase.