[Au₁₄(PPh₃)₈(NO₃)₄]: An Example of a New Class of Au(NO₃)‐Ligated Superatom Complexes

Abstract

Ultrasmall gold nanoparticles (usNPs) have been of considerable interest because of their unique properties, which arise from size quantization effects [1,2] and thus make them attractive for applications in different areas of nanoscience and nanotechnology. [3,4] Among usNPs of defined composition, and especially for gold clusters, an outstanding so-called "magic" stability has been observed for certain compositions. This stability has been explained through their specific geometric or electronic structure. In the full-shell cluster model, an usNP is considered as a cut-out of the bulk fcc structure. [5,6] Accordingly, a central metal atom is surrounded by shells of closely packed metal atoms, each shell having (10 n 2 +2) atoms, n indicating the number of shells. Clusters possessing fully occupied shells consist of 13, 55, 147, … atoms and are supposed to show high stability for geometric reasons, such as the well-studied Schmid cluster [Au 55 (PPh 3 ) 12 C l6 ]. [7] In another model, which goes back to the counting rules introduced by Mingos, [8] metal clusters are considered as superatom complexes formulated as [L S ·A N X M ] z with electron-withdrawing ligands X or weak Lewis base ligands L attached to the core with metal atoms A and an overall core charge z. [9,10] Accordingly, for Au the 6s electrons are counted and corrected by the number of electrons that are located at electron-withdrawing ligands and corrected by the charge of the cluster. The remaining 6s electrons are placed within the binding delocalized orbitals of the cluster, which is analogous to valence electrons of the atomic theory. Exceptional stability is associated with a total number of:

Molecular and Electronic Structure of the Cluster [Au8(PPh3)8](NO3)2

“…[38] Just recently, we revealed the extraordinary structure of [Au 14 (PPh 3 ) 8 (NO 3 ) 4 ], which has a shortest peripheral Au-Au distance of 2.5817(4) Å in addition to unique features like two neighbouring central gold atoms and Au(NO 3 ) ligands. [5] As expected, the P···P separation in [Au 8 …”

“…Owing to the specific electronic interactions in centred gold clusters, [26] the radial Au-Au bond lengths [2.5735 (7) 2 is the shortest radial inter-metal distance among a representative set of phosphine-stabilized gold clusters. [5] Shorter or similar nonradial separations have been found for the following compounds with different geometries: 2.561 Å for an axial separation in an Au 7 cluster, [28,35] 2.562 Å for a peripheral separation in an Au 3 cluster, [36] 2.565 Å for a peripheral separation in an Au 10 cluster [37] and 2.572(1) Å for a peripheral distance in an Au 3 cluster. [38] Just recently, we revealed the extraordinary structure of [Au 14 (PPh 3 ) 8 (NO 3 ) 4 ], which has a shortest peripheral Au-Au distance of 2.5817(4) Å in addition to unique features like two neighbouring central gold atoms and Au(NO 3 ) ligands.…”

“…[20] To analyse and understand the interplay between structural features and the electronic structures of usAuNPs, it would be highly desirable to combine the above-mentioned methods. This has partially been demonstrated for thiol-stabilized Au clusters, such as [Au 25 (SR) 18 ] - [15,21] or [Au 23 {SC(CH 3 ) 3 } 16 ], [22] or for Au clusters with a mixed thiol/phosphine ligand shell, such as [Au 25 (PPh 3 ) 10 (SR) 5 Cl 2 ] 2+ . [23] However, such a combination has rarely been applied to the analysis of electronic properties of smaller phosphine-stabilized usAuNPs or clusters consisting of 13 atoms or less.…”

Isolation, Optical Properties and Core Structure of a Water-soluble, Phosphine-stabilized [Au9]3+ Cluster

“…The radial Au-Au distances (2.617(11) and 2.681(12)Å) are shorter then the peripheral distances (2.776(13) and 2.802(13)Å), and the Au-P distances amount to 2.12(8) and 2.30(8)Å. All distances are within the typical range for gold clusters [6,19]. The stability of 1 can be explained by the formation of an ellipsoidal (2D) superatom complex which possesses an electron closure at 6 electrons within the binding cluster molecular orbitals [19].…”

“…All distances are within the typical range for gold clusters [6,19]. The stability of 1 can be explained by the formation of an ellipsoidal (2D) superatom complex which possesses an electron closure at 6 electrons within the binding cluster molecular orbitals [19]. Further details concerning the diffraction experiment are given in the Experimental Section.…”