Synthesis, structural characterization, and theoretical studies of goid(I) and gold(I)-gold(III) thiolate complexes: Quenching of gold(I) thiolate luminescence

Article abstract of DOI:10.1021/ic051168u

The gold(I) thiolate complexes [Au(2-SC₆H₄NH ₂)(PPh₃)] (1), [PPN][Au(2-SC₆H ₄NH₂)₂] (2) (PPN = PPh₃=N=PPh ₃), and [{Au(2-SC₆H₄NH₂)} ₂(μ-dppm)] (3) (dppm = PPh₂CH₂PPh ₂) have been prepared by reaction of acetylacetonato gold(I) precursors with 2-aminobenzenethiol in the appropriate molar ratio. All products are intensely photoluminescent at 77 K. The molecular structure of the dinuclear derivative 3 displays a gold-gold intramolecular contact of 3.1346-(4) A. Further reaction with the organometallic gold(III) complex [Au(C ₆F₅)₃(tht)] affords dinuclear or tetranuclear mixed gold(I)-gold(III) derivatives with a thiolate bridge, namely, [(AuPPh ₃){Au(C₆F₅)₃}(μ₂-2- SC₆H₄NH₂)] (4) and [(C₆F ₅)₃Au(μ₂-2-SC₆H ₄NH₂)(AudppmAu)(μ₂-2-SC₆H ₄NH₂)Au(C₆F₅)₃] (5). X-ray diffraction studies of the latter show a shortening of the intramolecular gold(I)-gold(I) contact [2.9353(7) or 2.9332(7) A for a second independent molecule], and short gold(I)-gold(III) distances of 3.2812(7) and 3.3822(7) A [or 3.2923(7) and 3.4052(7) A] are also displayed. Despite the gold-gold interactions, the mixed derivatives are nonemissive compounds. Therefore, the complexes were studied by DFT methods. The HOMOs and LUMOs for gold(I) derivatives 1 and 3 are mainly centered on the thiolate and phosphine (or the second thiolate for complex 2), respectively, with some gold contributions, whereas the LUMO for derivative 4 is more centered on the gold(III) fragment. TD-DFT results show a good agreement with the experimental UV-vis absorption and excitation spectra. The excitations can be assigned as a S → Au-P charge transfer with some mixture of LLCT for derivative 1, an LLCT mixed with ILCT for derivative 2, and a S → Au...Au-P charge transfer with LLCT and MC for derivative 3. An LMCT (thiolate → Au^III mixed with thiolate → Au-P) excitation was found for derivative 4. The differing nature of the excited states [participation of the gold(III) fragment and the small contribution of sulfur] is proposed to be responsible for quenching the luminescence.