The thermochemical properties of gas-phase transition metal ion complexes

Abstract

Gas phase ion clustering reactions of the form ${\mathrm{A}}^{+}(\mathrm{L}{)}_n+\mathrm{L}\rightleftarrows \mathrm{A}\mathrm{\hspace{0.17em}+(}\mathrm{L}{)}_{\text{n+1}}$ 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 ${\mathrm{Ag}}^{+}$ ion with $\text{n=0\hspace{0.17em}}\mathrm{to}5$ and the ${\mathrm{Cu}}^{+}$ ion with $\text{n=2\hspace{0.17em}}\mathrm{to}\text{4,}$ ammonia about the ${\mathrm{Ag}}^{+}$ and ${\mathrm{Cu}}^{+}$ ions from $\text{n=1}$ and $\text{n=2\hspace{0.17em}}\mathrm{to}\text{4,}$ respectively, and pyridine about the ${\mathrm{Ag}}^{+}$ and ${\mathrm{H}}^{+}$ ion from $\text{n=2}$ and $\text{n=1\hspace{0.17em}}\mathrm{to}\text{\hspace{0.17em} 3,}$ 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.