Silver(I) Clusters with Carba-closo-dodecaboranylethynyl Ligands: Synthesis, Structure, and Phosphorescence.

Salts of anionic silver(I) clusters with the carba-closo-dodecaboranylethynyl ligand were obtained from {Ag-2(12-C C-closo-1-CB11H11)}(n), selected pyridines, and [Et4N]Cl or [Ph4P]Br. Salts of octahedral silver(I) clusters [Et4N](2)[Ag-6(12-C C-closo-1-CB11H11)(4)(4-X-C5H5N)(x)] were formed with pyridine (X=H, x=8), 4-methylpyridine (X=Me, x=8), and 4-cyanopyridine (X=CN, x=10). In contrast, 3,5-lutidine (3,5-Me2Py) did not result in salts of dianionic clusters, even in the presence of excess of [Et4N]Cl or [Ph4P]Br; instead salts of monoanionic Ag-7(I) clusters, [Et4N][Ag-7(12-C C-closo-1-CB11H11)(4)(3,5-Me2Py)(9)] and [Ph4P][Ag-7(12-C C-closo-1-CB11H11)(4)(3,5-Me2Py)(13)] were obtained. The Ag-7(I) cluster is pentagonal bipyramidal in the former, but is an edge-capped octahedron in the latter. The 4-methylpyridine and 3,5-lutidine complexes show green phosphorescence at room temperature. Although argentophilic interactions give rise to sufficient spin-orbit coupling for intersystem crossing S-1 -> T-n and moderate-to-high radiative rate constants, time-resolved measurements indicate that the quantum yields are greatly influenced by the pyridine ligands, which mainly determine the non-radiative rate constants. In addition, the crystal structures of [Ag-16(12-C C-closo-1-CB11H11)(8)(Py)(9.25)(CH3CN)(2)(CH2Cl2)(0.75)]center dot CH2Cl2, [Ag-8(12-C C-closo-1-CB11H11)(4)(Py)(12)], [Ag-10(12-C C-closo-1-CB11H11)(4)(4-MePy)(10)Br-2], [Ag-7(12-C C-closo-1-CB11H11)(3)(4-tBuPy)(11)Cl]center dot(4-tBuPy), and [Ag-9(12-C C-closo-1-CB11H11)(4)(3,5-Me2Py)(11)Cl] were elucidated.