Silver Alkynyl-Phosphine Clusters: An Electronic Effect of the Alkynes Defines Structural Diversity

The face-capping triphosphine, 1,1,1-tris­(diphenyl­phos­phino)­methane
(tppm), together with bridging alkynyl ligands and the counterions,
facilitates the formation of a family of silver complexes, which adopt
cluster frameworks of variable nuclearity. The hexanuclear compounds
[Ag6­(C2­C6H4-4-X)3­(tppm)2­(An–)3] (X = H (1), CF3 (2), OMe (3), An– = CF3SO3–; X = OMe (4), An– = CF3COO–) are produced for the electron-accepting
to moderately electron-donating alkynes and the appropriate stoichiometry
of the reagents. 1 and 3 undergo an expansion
of the metal core when treated with 1 equiv of Ag+ to give
the species [Ag7­(C2­C6H4-4-X)3­(tppm)2­(CF3­SO3)3]­(CF3­SO3) (X = H (5), OMe (6)). The electron-donating
substituent (X = NMe2) particularly favors this Ag7 arrangement (7) that undergoes geometry changes
upon alkynylation, resulting in the capped prismatic cluster [Ag7­(C2­C6H4-4-NMe2)4­(tppm)2­(CF3­SO3)]­(CF3­SO3)2 (8). Alternatively, for the aliphatic tBu-alkyne, only the octanuclear complex [Ag8­(C2But)4­{(PPh2)3­CH}2­(CF3­SO3)2]­(CF3­SO3)2 (9) is observed. The structures
of 1–4 and 6–9 were determined by X-ray diffraction analysis. In solution,
all the studied compounds were found to be stereochemically nonrigid
that prevented their investigation in the fluid medium. In the solid
state, clusters 2, 3, 5–8 exhibit room temperature
luminescence of triplet origin (maximum Φem = 27%,
λem = 485–725 nm). The observed emission is
assigned mainly to [d(Ag) → π*­(alkyne)]
electronic transitions on the basis of TD-DFT computational analysis.