Endohedrally Doped Cage Clusters

Abstract

The discovery of carbon fullerene cages and their solids opened a new avenue to build materials from stable cage clusters as “artificial atoms” or “superatoms” instead of atoms. However, cage clusters of other elements are generally not stable. In 2001, ab initio calculations showed that endohedral doping of Zr and Ti atoms leads to highly stable Zr@Si16 fullerene and Ti@Si16 Frank–Kasper polyhedral clusters with large HOMO–LUMO gaps. In 2002, Zr@Ge16 was shown to form a Frank–Kasper polyhedron, suggesting the possibility of designing novel clusters by tuning endohedral and cage atoms. These results were subsequently confirmed from experiments. In the past nearly two decades, many experimental and theoretical studies have been carried out on different clusters, and many very stable cage clusters with possibly high abundance have been found by endohedral doping. Indeed in 2017, Ta@Si16 and Ti@Si16 cage clusters have been synthesized in bulk quantity of about 100 mg using a dry-chemistry method, giving rise to a new hope of developing cluster-based materials in macroscopic quantity besides the well-known C60 fullerene solid. Also, wet-chemistry methods have been used to synthesize endohedrally doped clusters as well as ligated clusters and their solids, which auger well for the development of novel nanostructured materials using atomically precise clusters with unique properties. In this comprehensive review, we present results of many such developments in this fast-growing field including (i) endohedrally doped Al, Ga, and In clusters, (ii) small endohedral carbon fullerene cages with ≤ 28 carbon atoms, (iii) metal doped boron cages, (iv) endohedrally doped cages of group 14 elements (Si, Ge, Sn, and Pb), (v) coinage metal (Cu, Ag, Au) cages doped with a transition metal atom as well as their ligated clusters and crystals, (vi) endohedrally doped cages of compound semiconductors, and (vii) multilayer Matryoshka cages and core–shell structures. In a large number of cases, we have performed ab initio calculations to present updated results of the most stable atomic structures and fundamental electronic properties of the endohedrally doped cage clusters. We discuss electronic, magnetic, optical, and catalytic properties in order to shed light on their potential applications. The stability of the doped cage clusters has been correlated to the concept of filling the electronic shells for superatoms such as within a spherical potential model and also using various electron counting rules including Wade–Mingos rules, systems with 18 and 32 electrons, and the spherical aromaticity rule. We also discuss cluster–cluster interaction in cluster dimers and assemblies of some of the promising doped cage clusters in different dimensions. Finally, we give a perspective of this field with a bright future.

Superatomic Signature and Reactivity of Silver Clusters with Oxygen: Double Magic Ag 17 – with Geometric and Electronic Shell Closure

“…Within the framework of the near free-electron gas (NFEG) theory 10 of metals, the empirical jellium model for metal clusters as introduced by Knight et al 11 unambiguously explains the observation of the magic numbers of 2, 8, 20, 40, 70, and 112 in sodium clusters corresponding to electronic shell closure on the basis of spherical harmonic potential. Furthermore, the Clemenger-Nilsson cluster model allows for prolate/oblate ellipsoidal distortion (or anharmonic oscillator distortion), 12,13 and enables us to rationalize stable clusters with altered subshells from prolate to oblate and subsequently a series of magic valence electron counts, that is, 2,8,18,20,34,40,58,70,92,112, and so forth. 10,12 As an important coinage metal element, the silver atom has a closed d shell and a single s valence electron, similar to alkali metals.…”

“…Besides electron count rules, 18,19 geometry is also an important factor that determines the stability of metal clusters. For example, those of favorable geometry such as Mackay icosahedra often find prominent stability.…”

Prediction of unexpected BnPn structures: promising materials for non-linear optical devices and photocatalytic activities

“…64 The evidence for our predicted -B 24 P 24 cluster is the encapsulation of transition metal in fullerene-like boron cages. [65][66][67] Yanming Ma and coworkers 65 predicted transition metal-doped B 24 clusters using first-principles swarm-intelligence-based structure searches. They found that the low-lying energy structures were generally cage-like structure.…”

TM4B180/− (TM = Hf, Ta, W, Re, Os): new structure construction with TM doped B wheel units

“…Due to the characteristic of electron deciency, B aggregates into various structures by sharing electrons and easily forms multicenter-two electron (mc-2e) bonds, which lead to various cluster structures. [1][2][3] In the past decade, combining experimental and theoretical calculations, it was found that small and medium-sized pure B clusters could have the planar, [4][5][6] quasi-planar, [7][8][9] double ring, 10,11 cage-like, [12][13][14][15] bilayer, 16,17 and core-shell 18 structures. The B n À clusters possess the planar or quasi-planar structures form up to the size of n $ 38, whereas the neutral counterparts from n ¼ 20 exhibit a transition from the planar to the double-ring tubular shape.…”