Generation of Small Gold Clusters with Unique Geometries through Cluster-to-Cluster Transformations: Octanuclear Clusters with Edge-sharing Gold Tetrahedron Motifs

摘要

Molecular gold clusters with defined nuclearity and geometrical structures have attracted continuing interest, due not only to the fundamental aspects of their unique nuclearity-and structure-dependent optical and electronic properties, but also to their potential in the development of novel nanomaterials and catalysts. Phosphine-coordinated small gold clusters (Au_n) with core nuclearities (n) ranging from 6 to 13, which form one of the major cluster families, are typical examples. X-ray crystallographic studies have shown that these clusters generally adopt toroidal or sphere-like structures due to prominent aurophilic interactions involving the central gold atom. Examples of linear edge-shared arrays of simple polyhedra have been limited to date, but recent theoretical studies have predicted that such core structures can be formed when coupled with appropriate surrounding shell (ligand) modules. In this relation, current developments in cluster synthetic methods have shown the utility of multidentate ligands for selective formation of particular geometrical structures. Herein, we report that the use of a diphosphine ligand in a cluster-to-cluster transformation through a growth/etching process leads to facile generation of two novel cluster cations [Au8(dppp)4Cl2]~(2+) (2) and [Au8-(dppp)4]~(2+) (4; dppp = 1,3-bis(diphenylphosphino)propane). Structural studies of these clusters revealed their unprecedented Au8 core geometries containing edge-fused gold tetrahedron motifs, which are isomeric with each other. We also highlight their geometry-dependent visible absorption and emission properties, and the selective optical response of 2 towards mercury ions.