Incompletely condensed silsesquioxanes, R7Si7O9(OH)(3) (R = cyclo-C5H9, iso-C4H9), react with trans- PtI(Ph)(L)(2)] (L = PEt3, PMe2Ph) at room temperature in the presence of Ag2O to yield platinum complexes with a monodentate O-coordinated silsesquioxane, trans-[Pt{O10Si7R7(OH)(2)}(Ph)(L)(2)] (1a: R = cyclo-C5H9; L = PEt3, 1b: R = iso-C4H9; L = PEt3, 2a: R = cyclo-C5H9; L = PMe2Ph, 2b: R = iso-C4H9; L= PMe2Ph). Reactions of silsesquioxanes with trans-[ PtI(Ph)(PPh3)(2)] in the presence of Ag2O at 55 degrees C afford unexpected Pt-Ag heterobimetallic complexes, [Pt{O11Si7R7(OH)(AgPPh3)}(Ph)(PPh3)] (3a: R = cyclo-C5H9, 3b: R = iso-C4H9), and a hydroxo-bridged dinuclear platinum complex, anti-[{PtPh- PPh3)}(2)(mu-OH)(2)] (4). These complexes were isolated and characterized by X-ray crystallography and H-1, P-31, Si-29, and C-13 NMR spectroscopy. The crystal structures of 3a and 3b show a square-planar coordination around the Pt center bonded to Ph, PPh3, and bidentate O, O-coordinated silsesquioxane. One of the coordinated oxygen atoms is also bound to the AgPPh3 group.