Synthesis and Optical Properties of a Dithiolate/Phosphine-Protected Au₂₈ Nanocluster

While monothiols and simple phosphines are commonly exploited for size-controlled synthesis of atomically precise gold nanoclusters (NCs), dithiols or dithiol-phosphine combinations are seldom applied. Herein, we used a dithiol (benzene-1,3-dithiol, BDT) and a phosphine (triphenylphosphine, TPP) together as ligands and synthesized an atomically precise gold NC with the formula [Au₂₈(BDT)₄(TPP)₉]²⁺. This NC exhibited multiple absorption features and a charge of +2, which are distinctly different from the reported all-thiolated [Au₂₈(SR)₂₀]⁰ NC (SR: monothiolate). The composition of [Au₂₈(BDT)₄(TPP)₉]²⁺ NC was deduced from high-resolution electrospray ionization mass spectrometry (ESI MS) and it was further corroborated by thermogravimetric analysis (TGA). Differential pulse voltammetry (DPV) revealed a HOMO–LUMO gap of 1.27 eV, which is in good agreement with the energy gap of 1.3 eV obtained from its UV–vis spectrum. The successful synthesis of atomically precise, dithiol-protected Au₂₈ NC would stimulate theoretical and experimental research into bidentate ligands as a new path for expanding the library of different metal NCs, which have so far been dominated by monodentate thiols