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[Se ₂P(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 Ag ₁₁Se 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(μ ₉-Se)(μ₃-Br)₃{Se₂P(O ⁱPr)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.