Читать книгу Superatoms - Группа авторов - Страница 28

In this chapter we have focused on the design of superatoms, which are atomic clusters of specific size and composition and whose chemistry mimics that of the atoms in the periodic table. The concept of superatoms is that their free electrons occupy a new set of orbitals that are defined by the entire group of atoms in the cluster, instead of by each atom separately. If these superatomic orbitals have the same symmetry as that of the atoms, one can think of a new class of materials with superatoms as the building blocks. Because of their specific size, cluster‐assembled materials may have properties different from those of the corresponding atom‐assembled materials. A classic example is C₆₀ fullerene‐based material vs diamond and graphite. All are made of only carbon atoms but their properties are very different because of the way carbon atoms are arranged.

The central question is how to design these superatoms so that they are stable and maintain their structure when assembled. We discussed various electron‐counting rules that have been used for nearly a century to explain the stability of atoms and the compounds they form. Just as superatomic orbitals mimic atomic orbitals, it is expected the same electron‐counting rules that apply to atoms may also apply to superatoms. Indeed, we demonstrated how the octet rule for low atomic number species, the 18‐electron rule for transition metals, the 32‐electron rule for rare earth metals, the Wade‐Mingos rule for boron‐based systems, and the aromaticity rules for organic molecules can be used to design not only stable neutral but anionic species. More importantly, we demonstrated how multiple electron‐counting rules can be used simultaneously to design negative ions carrying up to five extra electrons that are stable against fragmentation or auto‐ejection of the electron.

In Chapter 10, we will discuss how the superatoms can be used to promote unusual chemistry such as making noble gas atoms form chemical bonds at room temperature and accessing high oxidation states of metal atoms. The potential of cluster‐assembled materials in storing hydrogen, catalyzing reactions, serving as building blocks of super‐ and hyper‐salts, electrolytes in Li‐ and Na‐ion batteries, and moisture‐insensitive hybrid perovskite‐based solar cells is also discussed.