The (3)[nd sigma*(n+1)p sigma] 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), ClO4- (2), OTf- (3), PF6- (4), SCN-(5)1, [Ag-3(dcmp)(2)][ClO4](3) (6), and [Ag-3(dcmp)(2)Cl-2][ClO4] (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 rim, 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)[5d sigma*6p sigma] excited state of [Au-3(dcmp)(2)](3+), whereas the latter is attributed to an exciplex formed between the (3)[5d sigma*6p sigma] excited state of [Au-3(dcmp)(2)](3+) and the counterions. In solid state, complex [Ag-3(dcmp)(2)]-[ClO4](3) (6) displays an intense emission band at 375 nm with a Stokes shift of approximate to 7200 cm(-1) from the (1)[4d sigma*-> 5p sigma] absorption band at 295 nm. ne 375 nm emission band is assigned to the emission directly from the (3)[4d sigma*-> 5p sigma] 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 metal center dot center dot center dot anion contacts. The emission energies are extrapolated to be 71.5 and 446 nm for the infinite linear Au-I and Ag-I chains, respectively, at metal center dot center dot center dot metal distances of about 2.93-3.02 angstrom. A QM/MM calculation on the model [Au-3(dcmp)(2)Cl-2](+) system, with Au center dot center dot center dot Cl contacts of 2.90-3.10 angstrom, gave optimized Au center dot center dot center dot Au distances of 2.99-3.11 angstrom 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 center dot center dot center dot Au-I interactions.