Tetranuclear Copper(I) Iodide Complexes of Chelating Bis(1-benzyl-1H-1,2,3-triazole) Ligands: Structural Characterization and Solid State Photoluminescence

A series of tetranuclear Cu₄I₄(L_n)₂ clusters (1−3) supported by the chelating 4,4′-(4,5-diX-1,2-phenylene)bis(1-benzyl-1H-1,2,3-triazole) ligands (L1, X = H; L2, X = CH₃; L3, X = F) have been prepared. Crystal structure determinations have shown that the clusters adopt a distorted “step-type” geometry in which the triazole ligands exhibit both chelating and bridging coordination modes to Cu(I) ions. When L3 was employed in a 3:2 CuI/L3 ratio, a crystalline product, 4, was obtained. Product 4 is actually a 1:1 cocrystallization of the tetranuclear cluster 3 (denoted 4a) and the dinuclear Cu₂I₂(L3)₂ complex (4b). X-ray structures of 1, 2, and 4 show the presence of close Cu···Cu contacts in the tetranuclear and dinuclear forms. ¹H NMR experiments indicate that rapid exchange occurs in these systems. All clusters are brightly luminescent in the solid state at 77 K and at room temperature with λ_max = 495−524 nm. Emission intensity decays fit a single exponential with lifetimes on the order of 10 to 35 microseconds at room temperature and 90 to 140 microseconds at 77 K. The origin of emission is tentatively assigned as a metal-to-ligand phenylene π* charge transfer.