SYNTHESES, CHARACTERIZATIONS, LUMINESCENCE PROPERTIES, AND ELECTRONIC-STRUCTURES OF GOLD(I) BIS(PHOSPHINE)-XANTHATE COMPLEXES

Syntheses, structures and photophysical properties of some bis(phosphine) xanthate complexes, L2AuS2COR, L = Ph3P, CEP(tris(cyanoethyl)phosphine) are described. Extended Huckel and Fenske-Hall molecular orbital (MO) calculations indicate that bending activates the gold(I) center for interaction with nucleophiles. Experimentally, it is observed that the compound with the smaller P-Au-P angle (Ph3P) also shows the shortest Au-S distance. In fact, the (CEP)2AuS2COEt complex has two nearly identical Au-S distances at 2.745(2) and 2.934(2) angstrom, which are 0.2 angstrom longer than the short Au-S distance, 2.530(2) angstrom, in the (Ph3P)2AuS2COEt complex. The absorption spectra of the complexes show a moderately intense band around 306 nm (epsilon = (1.5-3.0) x 10(4) M-1 cm-1) and a weak band al ca. 390 nm (epsilon = 100 M-1 cm-1). The perturbation of the KS2COR ''free'' ligand anion absorption bands in CH3CN shifts the high-energy band slightly to the blue while the low-energy band significantly blue shifts. Spectral changes observed by the systematic variation of the R groups on the xanthate and by solvent variation studies suggest that the high energy band is a pi-pi* transition localized on the xanthate ligand. Each complex luminesces as a solid and in solution. Lifetimes for the solids are nanosecond in duration. Excitation spectra resemble absorption spectra. It is believed that the luminescence in these mononuclear gold(I) complexes originates from ligand excitation centered in the n-pi* transition. Complex 2, (CEP)2AuS2COEt, crystallizes in the monoclinic space group P2(1)/c (No. 14), with a = 11.538(2) angstrom, b = 20.302(4) angstrom, c = 11.565(1) angstrom, beta = 116.62(1)degrees, Z = 4, and R = 0.0325. Compound 4, (Ph3P)2AuS2COEt, crystallizes in the triclinic space group P1BAR (No. 2), with a = 10.316(3) angstrom, b = 13,058(2) angstrom c = 14.039(4) angstrom, alpha = 88.070, beta = 74.40-degrees, gamma = 76.59(1)degrees, Z = 2, and R = 0.0273.