From isosuperatoms to isosupermolecules: new concepts in cluster science

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 Au13(5+) 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 Ag22(12+) supermolecule formed by two Ag13(8+) 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)10Cl4(2+) and Au30S(StBu)18 to illustrate two Au20(6+) 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.