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 {Ag₂ (12-C≡C-closo-1-CB₁₁ H₁₁ )}_n , selected pyridines, and [Et₄ N]Cl or [Ph₄ P]Br. Salts of octahedral silver(I) clusters [Et₄ N]₂ [Ag₆ (12-C≡C-closo-1-CB₁₁ H₁₁ )₄ (4-X-C₅ H₅ N)_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-Me₂ Py) did not result in salts of dianionic clusters, even in the presence of excess of [Et₄ N]Cl or [Ph₄ P]Br; instead salts of monoanionic Ag^I₇ clusters, [Et₄ N][Ag₇ (12-C≡C-closo-1-CB₁₁ H₁₁ )₄ (3,5-Me₂ Py)₉ ] and [Ph₄ P][Ag₇ (12-C≡C-closo-1-CB₁₁ H₁₁ )₄ (3,5-Me₂ Py)₁₃ ] were obtained. The Ag^I₇ 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 S₁ →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 [Ag₁₆ (12-C≡C-closo-1-CB₁₁ H₁₁ )₈ (Py)_9.25 (CH₃ CN)₂ (CH₂ Cl₂ )_0.75 ]⋅CH₂ Cl₂ , [Ag₈ (12-C≡C-closo-1-CB₁₁ H₁₁ )₄ (Py)₁₂ ], [Ag₁₀ (12-C≡C-closo-1-CB₁₁ H₁₁ )₄ (4-MePy)₁₀ Br₂ ], [Ag₇ (12-C≡C-closo-1-CB₁₁ H₁₁ )₃ (4-tBuPy)₁₁ Cl]⋅(4-tBuPy), and [Ag₉ (12-C≡C-closo-1-CB₁₁ H₁₁ )₄ (3,5-Me₂ Py)₁₁ Cl] were elucidated.