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 [Au-28(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 [Au-28(SR)(20)](0) NC (SR: monothiolate). The composition of [Au-28(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 L27 eV, which is in good agreement with the energy gap of 1.3 eV obtained from its UV-vis spedfunl. The successful synthesis of atomically precise, dithiol-protected Au-28 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.