SOLID-STATE EXAFS AND LUMINESCENCE STUDIES OF NEUTRAL, DINUCLEAR GOLD(I) COMPLEXES - GOLD(I)-GOLD(I) INTERACTIONS IN THE SOLID-STATE

A series of neutral, dinuclear gold(I) complexes, containing phosphine and thiolate ligands, have been studied by EXAFS and luminescence spe ctroscopy. Gold(I)-gold(I) interactions are detected for the first tim e by EXAFS studies on solid samples at liquid helium temperature. A st rong, distinct peak at 1.90 +/- 0.02 Angstrom, assigned to Au-P and Au -S bonds, appears in the Fourier transform for complexes 1-8. A less i ntense peak appears for complexes 2-6 at 2.8 Angstrom with the amplitu de maximizing toward high k characteristic of a gold backscattering at om. The calculated EXAFS results indicate gold(I)-gold(I) distances ra nging from 3.0 to 3.2 Angstrom for complexes 2-6. In contrast, no gold (I)-gold(I) interactions are detected for complexes 1, 7, and 8. The A u-Au and Au-P(S) distances calculated by EXAFS are similar to those me asured by X-ray diffraction. All of the neutral, dinuclear gold(I) com plexes luminesce at room temperature in the solid state. The Stokes sh ifts average 6 x 10(3) cm(-1) and are indicative of a large distortion in the excited state compared to the ground state. Spectral acquisiti on using time delays of 10-50 mu s confirms the phosphorescent nature of the emission. The origin of the luminescence of complexes 1-8 is co nsistent with a S --> Au CT excited state that is perturbed by substit uent electronic effects leading to the red shift in emission for 5-8 r elative to 1-4. There is no correlation between gold(I)-gold(I) bondin g and the energy or band shape of the excitation and emission of 1-8. The luminescence and EXAFS results taken together demonstrate that a g old(I)-gold(I) interaction is not a necessary condition for luminescen ce. Further, the presence of a gold(I)-gold(I) interaction does not si gnificantly perturb the luminescence in this series of gold(I) complex es. [Au-2(p-tc)(2)L]: P-tc = p-thiocresol; L = 1,2-bis(diphenylphosphi no)ethane (1), 1,3-bis(diphenylphosphino)propane (2), 1,4-bis(diphenyl phosphino)butane (3), 1,5-bis(diphenylphosphino)pentane (4). [Au(L)(pd t)Au]: pdt = 1,3-propanedithiol; L = 1,2-bis(diphenylphosphino)ethane (5), 1,3-bis(diphenylphosphino)propane (6), 1,4-bis(diphenylphosphino) butane (7), 1,5-bis(diphenylphosphino)pentane (8).