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

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posted on 11.01.2017, 14:19 by Yi-Ting Chen, Ilya S. Krytchankou, Antti J. Karttunen, Elena V. Grachova, Sergey P. Tunik, Pi-Tai Chou, Igor O. Koshevoy
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 14 and 69 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, 58 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.