Three clusters [Ag-11(mu(9)-Se)(mu(3)-I)(3){Se2P(OR)(2)}(6)] (R = Et, 1; Pr-i, 2; Bu-2, 3) were isolated from the reaction of [Ag(CH3CN)(4)](PF6), NH4[Se2P(OR)(2)], and Bu4NI in a molar ratio of 4:3:1 in CH2Cl2 in 47-55% yield. Compounds 1 and 2 can also be synthesized with high yield from the reaction of Ag-10(Se)[Se2P(OR)(2)](8) with 8 equiv of Bu4NI. In the positive fast atom bombardment mass spectra of 1-3, two major peaks that correspond to the intact molecule with the loss of an iodide ion, [Ag-11(mu(9)-Se)(mu(3)-I)(2){Se2P(OR)(2)}(6)](+), and a diselenophosphate ligand, [Ag-11(mu(9)-Se)(mu(3)-I)(3){Se2P(OR)(2)}(5)](+), were identified. Single-crystal X-ray analyses of 2 and 3 reveal an Ag11Se core stabilized by three iodide anions and six diselenophosphato ligands in a tetrametallic tetraconnective (mu(2),mu(2)) coordination mode. The central core adopts the geometry of a 3,3,4,4,4-pentacapped trigonal prism with a selenium atom in the center. In addition, weak intermolecular Se center dot center dot center dot I interactions exist in 2 and form a one-dimensional polymeric chain structure. Furthermore, all compounds exhibit orange-red luminescence in both the solid state and solution.