Self-assembly between Ag+ and [PW11NbO40](4-) in N- and O-donor solvents (nitriles and amides) has been studied. In the case of dimethylformamide (DMF), formation of a yellow [Ag-4(DMF)(12)][PW11NbO40] (1a) metastable phase and a colorless [Ag-4(DMF) [PW11NbO40] (1) stable phase was observed. In acetonitrile (CH 3 CN), the product was [Ag(CH3CN)(4)](2) {[Ag(CH3CN)(3)](2) [PW11NbO40]} (2a). By contrast, [SiW12O40](4-) of the same size and charge as [PW11NbO40](4-) produces [Ag(CH3CN)(3)](4) [SiW12O40] (3a). Partial desolvation of 2a and 3a leads to Ag-4[PW11NbO40]center dot 7.5CH(3) CN (2) and Ag-4[SiW12O40]center dot 7.5CH(3)CN (3), respectively. The CH3CN molecules in the structure of 2 are labile, and this compound was used as the starting material to study solvent-exchange processes in N-methyl-2-pyrrolidone (NMP), dimethylacetamide (DMA), diethylformamide (DEF), and benzonitrile (PhCN) solutions. These solvent reactions yield [Ag(DMA)(4)][Ag-3 (DMA)(6)][PW11NbO40] (4), [Ag-2(NMP)(4)(CH3CN)](2)[PW11NbO40]center dot 1.3NMP (5a), [Ag NMP)(5)](2)[PW11NbO40] (5b), Ag-4[PW11NbO40]-9.5DEF (6), and [Ag(PhCN)(4)](2)[{Ag(PhCN)(3)}(2)PW11NbO40] (7). All products were isolated and characterized by single-crystal X-ray diffraction (except for 2 and 3), IR, elemental analysis, and thermogravimetric analysis techniques. The O-donor solvents favor polynuclear, solvent-bridged cationic aggregates. In the case of DMF, DMA, and DEF discrete, tri- and tetranuclear polycations are observed, while in the case of NMP, the formation of infinite polycationic structures takes place. By contrast, the N-donor solvents (CH3CN and PhCN) favor mononuclear cations, which can exist either as distorted tetrahedral, isolated [Ag(Solv)(4)](+) cations or as pseudotriangular {Ag(Solv)(3)}(+) units, additionally coordinated to a polyoxometalate. Screening of the luminescent properties for solid samples of 1-7 revealed that only 5a/5b and 7 are emissive. In particular, the sample containing 5a and 5b demonstrates longlived phosphorescence with a 30 ms lifetime.