Diphosphine-protected ultrasmall gold nanoclusters: opened icosahedral Au13 and heart-shaped Au8 clusters. Issue 5 (21st December 2017) - Zhang, Shan-Shan
Abstract : Two ultrasmall gold clusters, Au13 and Au8, were identified as a distorted I h icosahedral Au13 and edge-shared "core + 4 exo " structure Au8 S2 cores, respectively. They showed interesting luminescence and electrochemical properties. Abstract : Due to distinctive quantum confinement effects, ultrasmall gold nanoparticles usually exhibit interesting electronic structure and molecular-like properties. However, the lack of atomically-precise structural information makes the understanding of them almost impossible, such as understanding the relationships between their compositions and unique properties. Herein, by reducing a diphosphine Au I precursor (Au2 (dppm)2 Cl2 ; dppm = Ph2 PCH2 PPh2 ) with or without a S 2− releasing reagent, we enriched our knowledge of the members in the families of Au13 and Au8 by the structural determinations of two new dppm-protected gold nanoclusters, [Au13 (dppm)6 ] 5+ (SD/Au1 ) and [Au8 (dppm)4 S2 ] 2+ (SD/Au2 ), respectively. WithinSD/Au1, the Au13 kernel significantly deviates from the ideal I h icosahedron by the elongation of three surface Au–Au bonds to ∼3.5 Å, giving it C 3 symmetry, whereasSD/Au2 has a novel heart-shaped C 2 symmetric Au8 S2 core (central Au4 tetrahedron + two Au2 S units) protected by four μ2 -dppm ligands in the outer shell. Of note, SD/Au1 represents a rare Au13 nanocluster with an opened icosahedral geometry, andSD/Au2 shows a new edge-shared "core + 4 exo " structure type that has never been observed before. The electronic structures and optical absorption spectra of these systems are correlated with time-dependent density functional theory (TDDFT) calculations. Based on the spherical jellium model, the stability of the Au13 and Au8 nanoclusters can be ascribed to 8- and 2-electron superatoms with 1S 2 1P 6 and 1S 2 configurations, respectively. Interestingly, the clusterSD/Au2 exhibits bright yellow luminescence with an emission maximum at 591 nm that slightly hypsochromically shifts to 581 nm upon cooling to 93 K. Our findings not only enrich the family of diphosphine-protected ultrasmall gold nanoclusters, but also demonstrate the rich variations of gold kernels during the transformation from a simple Au I precursor to Au nanoclusters.