[Irs(CO)(22)](2-) was formed by surface-mediated synthesis by treatment of [Ir(CO)(2)(acac)] supported on uncalcined gamma-Al2O3 under 1 atm of CO at room temperature. The formation of [Ir-8(CO)(22)](2-) completes the synthesis of a family of iridium carbonyl clusters, including [Ir-4(CO)(12)], [HIr4(CO)(11)](-), [Ir-6(CO)(15)](2-), and [Ir-8(CO)(22)](2-), on the surface of gamma-Al2O3. The surface chemistry parallels known solution chemistry of the synthesis of the family of iridium carbonyls. The products formed are controlled largely by the basicity of the solution or surface, and the analogy between the solution and surface chemistry provides a preliminary, qualitative basis for characterizing the basicity of gamma-Al2O3 and other metal oxide samples. Decarbonylation of [Ir-8(CO)(22)](2-) on gamma-Al2O3 led to nearly uniform tetrahedral Ir-4 clusters; it is likely that the Ir-Ir single bond linking two iridium tetrahedral moieties in the precursor [Irs(CO)(22)](2-) on gamma-Al2O3 was broken during the decarbonylation.