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 (<b>1</b>), CF₃ (<b>2</b>), OMe (<b>3</b>), An^– = CF₃SO₃^–; X = OMe (<b>4</b>), An^– = CF₃COO^–) are produced for the electron-accepting to moderately electron-donating alkynes and the appropriate stoichiometry of the reagents. <b>1</b> and <b>3</b> 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 (<b>5</b>), OMe (<b>6</b>)). The electron-donating substituent (X = NMe₂) particularly favors this Ag₇ arrangement (<b>7</b>) that undergoes geometry changes upon alkynylation, resulting in the capped prismatic cluster [Ag₇­(C₂­C₆H₄-4-NMe₂)₄­(tppm)₂­(CF₃­SO₃)]­(CF₃­SO₃)₂ (<b>8</b>). Alternatively, for the aliphatic <i>^t</i>Bu-alkyne, only the octanuclear complex [Ag₈­(C₂Bu^<i>t</i>)₄­{(PPh₂)₃­CH}₂­(CF₃­SO₃)₂]­(CF₃­SO₃)₂ (<b>9</b>) is observed. The structures of <b>1</b>–<b>4</b> and <b>6</b>–<b>9</b> 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 <b>2</b>, <b>3</b>, <b>5</b>–<b>8</b> exhibit room temperature luminescence of triplet origin (maximum Φ_em = 27%, λ_em = 485–725 nm). The observed emission is assigned mainly to [<i>d</i>(Ag) → π*­(alkyne)] electronic transitions on the basis of TD-DFT computational analysis