From isosuperatoms to isosupermolecules: new concepts in cluster science

Abstract

As an extension of the superatom concept, a new concept “isosuperatom” is proposed, reflecting the physical phenomenon that a superatom cluster can take multiple geometrical structures with their electronic structures topologically invariant. The icosahedral and cuboctahedral Au₁₃⁵⁺ units in the Au₂₅(SCH₂CH₂Ph)₁₈⁻, Au₂₃(SC₆H₁₁)₁₆⁻ and Au₂₄(SAdm)₁₆ nanoclusters are found to be examples of this concept. Furthermore, two isosuperatoms can combine to form a supermolecule. For example, the structure of the {Ag₃₂(DPPE)₅(SC₆H₄CF₃)₂₄}²⁻ nanocluster can be understood well in terms of a Ag₂₂¹²⁺ supermolecule formed by two Ag₁₃⁸⁺ isosuperatoms. On the next level of complexity, various combinations of isosuperatoms can lead to supermolecules with different geometrical structures but similar electronic structures, i.e., “isosupermolecules”. We take two synthesized nanoclusters Au₂₀(PPhpy₂)₁₀Cl₄²⁺ and Au₃₀S(StBu)₁₈ to illustrate two Au₂₀⁶⁺ isosupermolecules. The proposed concepts of isosuperatom and isosupermolecule significantly enrich the superatom concept, give a new framework for understanding a wide range of nanoclusters, and open a new door for designing assembled materials.