Diphosphine-protected ultrasmall gold nanoclusters: opened icosahedral Au13 and heart-shaped Au8 clusters

摘要

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 (Au _(2) (dppm) _(2) Cl _(2) ; dppm = Ph _(2) PCH _(2) PPh _(2) ) with or without a S ~(2?) releasing reagent, we enriched our knowledge of the members in the families of Au _(13) and Au _(8) by the structural determinations of two new dppm-protected gold nanoclusters, [Au _(13) (dppm) _(6) ] ~(5+) ( SD/Au1 ) and [Au _(8) (dppm) _(4) S _(2) ] ~(2+) ( SD/Au2 ), respectively. Within SD/Au1 , the Au _(13) kernel significantly deviates from the ideal I _(h) icosahedron by the elongation of three surface Au–Au bonds to ～3.5 ?, giving it C _(3) symmetry, whereas SD/Au2 has a novel heart-shaped C _(2) symmetric Au _(8) S _(2) core (central Au _(4) tetrahedron + two Au _(2) S units) protected by four μ _(2) -dppm ligands in the outer shell. Of note, SD/Au1 represents a rare Au _(13) nanocluster with an opened icosahedral geometry, and SD/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 Au _(13) and Au _(8) nanoclusters can be ascribed to 8- and 2-electron superatoms with 1S ~(2) 1P ~(6) and 1S ~(2) configurations, respectively. Interestingly, the cluster SD/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.