Structure, Photophysical Properties, and DFT Calculations of Selenide-Centered Pentacapped Trigonal Prismatic Silver(I) Clusters

Undecanuclear silver clusters [Ag-11(mu(g)-Se)(mu(3)-Br)(3){Se2P(OR)(2)}(6)] (R = Et, Pr-1, Bu-2) were isolated from the reaction of [Ag(CH3CN)(4)](PF6), NH4[Se2P(OR)(2)], and Bu4NBr in a molar ratio of 4:3:1 in CH2Cl2 at -20 degrees C. Clusters were characterized by elemental analysis, NMR spectroscopy (H-1, P-31, and Se-77), positive FAB mass spectrometry, and X-ray crystallography of the isopropyl derivative, Structural elucidations revealed that the Ag11Se core geometry of clusters is a selenide-centered, slightly distorted 3,3,4,4,4-pentacapped trigonal prism surrounded by six diselenophosphato ligands, each in a tetrametallic tetraconnective (mu(2),mu(2)) coordination mode, and three mu(3)-bromide anions. All compounds exhibited orange luminescence both as a solid and in solution. The electronic structure of these clusters was studied by DFT calculations, and their optical properties were rationalized through a TDDFT investigation. The computed metrical parameters of the clusters were consistent with the corresponding X-ray data of [Ag-11(mu g-Se)(mu(3)-Br)(3){Se2P((OPr)-Pr-i)(2)}(6)]. The theoretical investigations affirmed that the low-energy absorptions as well as emissions were due to transitions from an orbital mostly of a selenophosphate ligand/central Se atom character to an orbital of metal character.