Systematics of stable copper and silver clusters protected by small bite chelating bidentate sulfur and selenium ligands related to their polyhedral cavities: analogies to aliphatic compounds and three-dimensional spherical aromatic systems

Abstract

Silver and copper clusters capped by external chelating dithiolate ligands can be classified according to the cavities in their central coinage metal polyhedra. Silver clusters composed exclusively of fused tetrahedra are analogous to simple saturated organic compounds. The only interstitial atom that can be fit into an Ag₄ tetrahedron is hydrogen. Silver polyhedra with larger trigonal prismatic or cubic cavities, including highly distorted cubic cavities, can accommodate halide and chalcogenide anions. The still larger 12-vertex icosahedral and cuboctahedral coinage metal cavities can accommodate oxoanions of the types SO₃²⁻ and SO₄²⁻ and their heavier congeners or alternatively interstitial coinage or platinum group metals leading to central M′@M₁₂ units. Copper clusters with central cuboctahedra and silver clusters with central icosahedra possessing interstitial metal atoms approximate sphericality and provide examples of electron-rich metal superatoms with an average metal oxidation state of less than +1. Such copper cluster superatoms have two extra electrons corresponding to a filled 1S² superatomic orbital. The silver cluster superatoms are electron richer with eight extra electrons corresponding to filled 1S² + 1P⁶ superatomic orbitals. In these silver clusters seven or eight faces of the central Ag₁₂ icosahedron are capped by additional silver atoms in order to provide these additional electrons.