The (3)[ndsigma*(n+1)psigma] emissions of linear silver(I) and gold(I) chains with bridging phosphine ligands

The complexes [Au(3)(dcmp)(2)][X](3) {dcmp=bis(dicyclohexylphosphinomethyl)cyclohexylphosphine; X=Cl(-) (1), ClO(4) (-) (2), OTf(-) (3), PF(6) (-) (4), SCN(-)(5)}, [Ag(3)(dcmp)(2)][ClO(4)](3) (6), and [Ag(3)(dcmp)(2)Cl(2)][ClO(4)] (7) were prepared and their structures were determined by X-ray crystallography. Complexes 2-4 display a high-energy emission band with lambda(max) at 442-452 nm, whereas 1 and 5 display a low-energy emission with lambda(max) at 558-634 nm in both solid state and in dichloromethane at 298 K. The former is assigned to the (3)[5dsigma*6psigma] excited state of [Au(3)(dcmp)(2)](3+), whereas the latter is attributed to an exciplex formed between the (3)[5dsigma*6psigma] excited state of [Au(3)(dcmp)(2)](3+) and the counterions. In solid state, complex [Ag(3)(dcmp)(2)][ClO(4)](3) (6) displays an intense emission band at 375 nm with a Stokes shift of approximately 7200 cm(-1) from the (1)[4dsigma*-->5psigma] absorption band at 295 nm. The 375 nm emission band is assigned to the emission directly from the (3)[4dsigma(*)5psigma] excited state of 6. Density functional theory (DFT) calculations revealed that the absorption and emission energies are inversely proportional to the number of metal ions (n) in polynuclear Au(I) and Ag(I) linear chain complexes without close metalanion contacts. The emission energies are extrapolated to be 715 and 446 nm for the infinite linear Au(I) and Ag(I) chains, respectively, at metalmetal distances of about 2.93-3.02 A. A QM/MM calculation on the model [Au(3)(dcmp)(2)Cl(2)](+) system, with Au...Cl contacts of 2.90-3.10 A, gave optimized Au...Au distances of 2.99-3.11 A in its lowest triplet excited state and the emission energies were calculated to be at approximately 600-690 nm, which are assigned to a three-coordinate Au(I) site with its spectroscopic properties affected by Au(I)...Au(I) interactions.