Polyicosahedricity: icosahedron to icosahedron of icosahedra growth pathway for bimetallic (AuAg) and trimetallic (AuAgM; M  Pt, Pd, Ni) supraclusters; synthetic strategies, site preference, and stereochemical principles

Abstract

In this review, syntheses and structural systematics of a series of vertex-sharing polyicosahedral clusters containing group 11 (Au,Ag,Cu) and group 10 (Pt,Pd,Ni) metals are discussed. This particular series of clusters follows a well-defined growth pathway in which the basic building block is the 13-atom centered icosahedron. The design rule is vertex sharing and the cluster “grows” by successive additions of icosahedral units via sharing of atoms. This cluster of clusters growth mechanism from a single icosahedron (13 atoms) to an icosahedron of icosahedra (127 atoms) parallels the atom-by-atom growth from a single atom to a 13-atom icosahedron and hence may be considered as a manifestation of the spontaneous self-organization and self-similarity aggregation process in the early stages of particle growth. This tendency to form polyicosahedral clusters may be termed polyicosahedricity. Recent developments in synthetic strategies and stereochemical principles of bi- and trimetallic vertex-sharing polyicosahedral clusters are highlighted with emphasis on (1) endo icosahedral chemistry by incorporating group 10 metals in the centers of the icosahedra, (2) exo icosahedral chemistry by capping the icosahedral faces with metal atoms or by “capturing” small molecules in the cluster cavities, and (3) framework icosahedral chemistry by changing the metal combination (group 11 metals) of the cluster architecture. Specifically, a new synthetic strategy based on “preformed clusters”, site preference rules, new concepts such as rotamerism and roulettamerism, and a new intracavity chemistry on a cluster surface resembling Venus flytrap are discussed. It is hoped that basic understanding of the stereochemical and bonding principles governing alloy formation in multimetallic clusters will lead to better electronic and stereochemical controls of their structures and reactivities and, ultimately, give rise to better design and manufacture or fabrication of structurally well-defined and functionally optimized nanoarchitecture, multimetallic catalysts, etc.