Homoleptic Copper( I), Silver( I), and Gold( I) Bisphosphine Complexes

A series of homoleptic copper(I), silver(I), and gold(I) complexes of two bisphosphine ligands {1,2-bis(diphenylphosphino)benzene, dppb; bis[2-(diphenylphosphino)phenyl]ether, POP} have been prepared. Whilst all three [M(dppb)(2)]BF4 complexes are tetracoordinate, this geometry is found only for the silver(I) complex with POP. Instead, [Cu(POP)(2)](+) and [Au(POP)(2)](+) adopt a trigonal coordination geometry with an uncoordinated phosphorus atom. A close inspection of the P-M bond lengths reveals an interesting trend. From the copper to silver and gold complexes, a substantial elongation is found. On the other hand, from the silver to gold compounds, a decrease in the M-P bond length is found. Indeed, gold(I) has a smaller van der Waals radius than silver(I) as a result of its peculiar relativistic effects. Electrochemical investigations revealed two oxidation processes for all of the [M(dppb)(2)]BF4 and [M(POP)(2)]BF4 complexes. The first oxidation is likely metal-centered, whereas the second one corresponds to ligand-centered processes in all cases. The emission properties of these compounds in solution, in frozen rigid matrices at 77 K, and in the solid state at room temperature have been systematically investigated. Although all of them are weak emitters in solution, remarkably high emission quantum yields were found in the solid state, in particular for [Cu(dppb)(2)]BF4 and [Ag(dppb)(2)]BF4. Finally, these two compounds were used for the fabrication of light-emitting devices. Interestingly, both the copper(I) and the silver(I) complex afford quite broad electroluminescence spectra with white light emission.