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

Undecanuclear silver clusters [Ag11(μ9-Se)(μ3-Br)3{Se2P(OR)2}6] (R = Et, iPr, 2Bu) 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 °C. Clusters were characterized by elemental analysis, NMR spectroscopy (1H, 31P, and 77Se), 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 (μ2, μ2) coordination mode, and three μ3-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 [Ag11(μ9-Se)(μ3-Br)3{Se2P(OiPr)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.