Luminescent Tetranuclear Silver(I) Arylacetylide Complexes Bearing Tricyclohexylphosphine Ligands: Synthesis, Molecular Structures, and Spectroscopic Comparison with Gold(I) and Copper(I) Arylacetylides

A series of luminescent tetranuclear silver(I) arylacetylides [Ag 4 { μ -(C⋮C) x C 6 H 4 R- p ) 4 }(PCy 3 ) y ] ( x = 1, y = 2, R = H ( 1 ), CH 3 ( 2 ), OCH 3 ( 3 ), C⋮CPh ( 5 ); x = 2, y = 4, R = H ( 4 )) were synthesized by treatment of tricyclohexylphosphine (PCy 3 ) with [Ag{(C⋮C) x C 6 H 4 R- p }] ∞ in dichloromethane in the absence of light, and their spectroscopic and photophysical properties have been investigated. The X-ray structure of 1 exhibits a planar parallelogram-like Ag 4 core and consists of [Ag(C⋮CPh) 2 ] and [Ag(PCy 3 )] fragments with phenylacetylide σ-coordinated to silver atoms in a μ 2 -bonding mode (mean asymmetric Ag−C(α) distances are 2.05 and 2.33 Å). For 2, 3, and 5, with different para substituents in the arylacetylide units, similar tetranuclear structures are observed. In contrast, the structure of 4 can be described as two interpenetrating tetrahedra of four silver atoms and four phenylbutadiynyl moieties forming a twisted cubane structure, with each silver atom further coordinated to a PCy 3 ligand. The electronic absorption spectra of 1 − 5 in CH 2 Cl 2 are dominated by strong, vibronically structured absorptions at 250−332 nm (ε 10 4 −10 5 dm 3 mol - 1 cm - 1 ) with vibrational spacings of 1420−2160 cm - 1 which are attributed to ν(C⋮C) or admixtures of acetylenic and aryl stretching frequencies. The solid-state emission spectra of 1 − 3 at 298 and 77 K show intense vibronically structured bands at 422−607 nm which are attributed to 3 (ππ*) excited states of the arylacetylide ligands. For 4, the solid-state emission is slightly red-shifted in energy from the 3 (ππ*) emission of the corresponding mononuclear [Au(PCy 3 )(C⋮C−C⋮CPh)] congener, whereas for 5, a red-shift in its emission is observed from that of 1 − 4 . A comparison between the emission of Cu(I), Ag(I), and Au(I) arylacetylides is made.