The Dawson-type P2W15Nb3O629- polyoxoanion-supported Re(CO)(3)(+) complex, [Re(CO)(3) . P2W15Nb3O62](8-) (1), has been synthesized and characterized in two different counter-cation compositions. The [(n-C4H9)(4)N](8)(8+) complex provides a highly soluble compound which exists as a single isomer in solution. The carbonyl stretching infrared frequencies suggest that the P(2)W(15)Nb3O(62)(9-) ligand serves as a strong electron donor to the Re(CO)(3)(+) fragment. The P2W15Nb3O629- polyoxoanion-supported Ir(CO)(2)(+) complex [Ir(CO)(2) . P2W15Nb3O62](8-) (2) has also been synthesized and characterized as its octakis(tetrabutylammonium), [(n-C4H9)(4)N](8)(8+), salt. This compound was characterized by NMR and IR, results which demonstrate that 2 also exists as a single isomer in solution. The [Ir(CO)(2) . P2W15Nb3O62](8-) complex is stable in the absence of water, but decomposes quickly in the presence of even 1 equiv of water. Attempted preparation of the analogous P2W15Nb3O629--supported Rh(CO)(2)(+) complex (3), while monitoring by P-31 NMR, revealed that this compound is unstable in solution at room temperature. In addition, we have discovered that added Na+ can induce the formation of non-C-3v symmetry isomers of supported Re(CO)(3)(+) and Ir(CO)(2)(+) and, by inference, supported Ir(1,5-COD)(+). When Na+ is removed from these systems by addition of Kryptofix[2.2.2], the non-C-3v isomers convert back to the single, C-3v isomer with heating, thereby providing a model system for the little studied mobility of RI(CO),,+ cations across a soluble-oxide surface. When [Rh(CO)(2) . P2W15Nb3O62](8-) is irradiated in the presence of hydrogen and cyclohexene a novel polyoxoanion-stabilized Rh-n(0) nanocluster is formed, results that bear a strong analogy to Yates’ work studying atomically-dispersed Rh(CO)(2)(+) on solid Al2O3 .10e Yates and co-workers observe that Rh(CO)(+). Al2O3 loses a CO upon photolysis, and that the resultant Rh(CO)(1)(+). Al2O3 is reduced under H-2 to form Rh(0), which in turn yields Rh-n(0) clusters on Al2O3-a process that, intriguingly, is largely reversible if CO is readded. Also briefly discussed is other relevant literature of solid-oxide-supported Re(CO)(3)(+) and M(CO)(2)(+) (M = Ir, Rh), literature that makes apparent the potential significance of these complexes as EXAFS and other spectroscopic models of solid-oxide-supported M(CO)(n)(+).