[Ag115S34(SCH2C6H4t Bu)47(dpph)6]: synthesis, crystal structure and NMR investigations of a soluble silver chalcogenide nanocluster

Abstract

With the aim to synthesize soluble cluster molecules, the silver salt of (4-(tert-butyl)phenyl)methanethiol [AgSCH₂C₆H₄^t Bu] was applied as a suitable precursor for the formation of a nanoscale silver sulfide cluster. In the presence of 1,6-(diphenylphosphino)hexane (dpph), the 115 nuclear silver cluster [Ag₁₁₅S₃₄(SCH₂C₆H₄^t Bu)₄₇(dpph)₆] was obtained. The molecular structure of this compound was elucidated by single crystal X-ray analysis and fully characterized by spectroscopic techniques. In contrast to most of the previously published cluster compounds with more than a hundred heavy atoms, this nanoscale inorganic molecule is soluble in organic solvents, which allowed a comprehensive investigation in solution by UV-Vis spectroscopy and one- and two-dimensional NMR spectroscopy including ³¹P/¹⁰⁹Ag-HSQC and DOSY experiments. These are the first heteronuclear NMR investigations on coinage metal chalcogenides. They give some first insight into the behavior of nanoscale silver sulfide clusters in solution. Additionally, molecular weight determinations were performed by 2D analytical ultracentrifugation and HR-TEM investigations confirm the presence of size-homogeneous nanoparticles present in solution.

Scheme 1. Synthesis of [Ag₁₁₅S₃₄(SCH₂C₆H₄ ^tBu)₄₇(dpph)₆] 1.

Fig. 1. Crystal structure of [Ag₁₁₅S₃₄(SCH₂C₆H₄ ^tBu)₄₇(dpph)₆] 1. Silver blue, silver (disordered) turquoise, sulfur (RS^–) yellow, sulfur (S^2–) (orange) phosphorous green, carbon black, hydrogen white.

Fig. 2. Top: Illustration of the inorganic cluster core of 1 with dpph ligands. Bottom: Space-filling model of the cluster surrounded by ^tBuC₆H₄CH₂S^– and dpph ligands.

Fig. 3. Cutout of the S-substructure within the Ag₁₁₅ cluster. Sulfide ions form two twofold bicapped hexagonal antiprisms, which blend into each other (blue). Taking into account further sulphur atoms, the polyhedron is extended by two more identical, but distorted antiprisms. Depicted S–S bonds do not represent covalent bonds. Full S-substructure (Fig. S14‡).

Fig. 4. ³¹P{¹H} NMR spectrum of 1 in CDCl₃.

Fig. 5. ³¹P/¹⁰⁹Ag gHSQC spectrum of 1 in CDCl₃ at 297 K.

Fig. 6. (a) Brightfield TEM image of the nanoparticles with an inset of the indexed SAED pattern. (b) HR-TEM micrograph of the nanoparticles clearly depicting the crystalline nature with an inset of the FFT from the marked area. (c) Particle size distribution.