The preparation and structural characterization of a novel intercluster compound, [{Au(PPh3)}(4)(mu(4)-O)](3)-[alpha-PW12O40](2) center dot 4EIOH (1), constructed between a tetrakis{triphenylphosphinegold(I)}oxonium cation and a saturated alpha-Keggin polyoxometalate (POM) are described. The tetragold(I) cluster oxonium cation was formed during the course of carboxylate elimination of a monomeric phosphinegold(I) carboxylate complex, i.e., [Au((R,S)-pyrrld)-(PPh3)] [(R,S)-Hpyrrld = (R,S)-2-pyrrolidone-5-carboxylic acid], in the presence of the free acid form of a Keggin POM, H-3[alpha-PW12O40]center dot 7H(2)O. The liquid liquid diffusion between the upper water/EtOH phase containing the Keggin POM and the lower CH2Cl2 phase containing the monomeric gold(I) complex gave a pure crystalline sample of 1 in good yield (42.1%, 0.242 g scale). Complex 1 was formed by ionic interaction between the tetragold(I) cluster cation and the Keggin POM anion. As a matter of fact, the POM anion in 1 can be exchanged with the BF4- anion using an anion-exchange resin (Amberlyst A-27) in BF4- form. By using other Keggin POMs, such as H-4[alpha-SRA(12)O(40)] center dot 10H(2)O and H-3[alpha-PMo12O40]center dot 14H(2)O, the same tetragold(I) cluster cation was also formed, i.e., in the forms of [{Au(PPh3)}(4)(mu(4)-O)](2)[alpha-SiW12O40]center dot 2H(2)O (2) and HAu(PPh3)}(4)(mu(4)-O)](3)[alpha-PMo12O40](2)center dot 3EtOH (3). Compounds 1-3, as dimethyl sulfoxide-soluble, EtOH- and Et2O-insoluble dark-yellowish white solids, were characterized by complete elemental analysis, thermogravimetric and differential thermal analyses, Fourier transform IR, X-ray crystallography, and solid-state (CPMAS P-31 and (29)i) and solution (P-31{H-1} and H-1) NMR spectroscopy. The molecular structures of 1 and 2 were successfully determined. The tetragold(I) cluster cation was composed of four PPh3Au1 units bridged by a central mu(4)-oxygen atom in the geometry of a trigonal pyramid or distorted tetrahedron.