Synthesis, Structural Characterization, and Theoretical Studies of Gold(I) and Gold(I)−Gold(III) Thiolate Complexes: Quenching of Gold(I) Thiolate Luminescence

Abstract

The gold(I) thiolate complexes [Au(2-SC₆H₄NH₂)(PPh₃)] (1), [PPN][Au(2-SC₆H₄NH₂)₂] (2) (PPN = PPh₃NPPh₃), and [{Au(2-SC₆H₄NH₂)}₂(μ-dppm)] (3) (dppm = PPh₂CH₂PPh₂) 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) Å. Further reaction with the organometallic gold(III) complex [Au(C₆F₅)₃(tht)] affords dinuclear or tetranuclear mixed gold(I)−gold(III) derivatives with a thiolate bridge, namely, [(AuPPh₃){Au(C₆F₅)₃}(μ₂-2-SC₆H₄NH₂)] (4) and [(C₆F₅)₃Au(μ₂-2-SC₆H₄NH₂)(AudppmAu)(μ₂-2-SC₆H₄NH₂)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) Å for a second independent molecule], and short gold(I)−gold(III) distances of 3.2812(7) and 3.3822(7) Å [or 3.2923(7) and 3.4052(7) Å] 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.