All-thiol-stabilized Ag44 and Au12Ag32 nanoparticles with single-crystal structures

Noble metal nanoparticles stabilized by organic ligands are important for applications in assembly, site-specific bioconjugate labelling and sensing, drug delivery and medical therapy, molecular recognition and molecular electronics, and catalysis. Here we report crystal structures and theoretical analysis of three Ag-44(SR)(30) and three Au12Ag32(SR)(30) inter-metallic nanoclusters stabilized with fluorinated arylthiols (SR = SPhF, SPhF2 or SPhCF3). The nanocluster forms a Keplerate solid of concentric icosahedral and dodecahedral atom shells, protected by six Ag-2(SR)(5) units. Positive counterions in the crystal indicate a high negative charge of 4(-) per nanoparticle, and density functional theory calculations explain the stability as an 18-electron superatom shell closure in the metal core. Highly featured optical absorption spectra in the ultraviolet-visible region are analysed using time-dependent density functional perturbation theory. This work forms a basis for further understanding, engineering and controlling of stability as well as electronic and optical properties of these novel nanomaterials.