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Progress in the Development of a Systematic Nanoperiodic Framework for Unifying Nanoscience
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Donald A. Tomalia, Shiv N. Khanna
Extensive research over the last four decades has shown that the fundamental electronic properties including ionization energy, electron affinity, chemical valence, reactivity, magnetic properties and optical properties of clusters can change strikingly by adding, removing or replacing even a single atom or by adding ligands. The characterization and cataloging all of the potential properties of different clusters is a daunting task, and the organization of the enormous numbers and varieties of clusters into a useful framework can be an important step toward design of cluster assemblies with selected properties. A simple and elegant framework in which clusters may be organized is by characterizing those whose properties and reactivity may be approximated by those of an atom and behave like a “superatom.” In the following, we outline the development of this conceptual framework.
Characterisation of superalkaline-earth-metal halides, hydroxide and chalcogenides
Published in Molecular Physics, 2018
Hai-di Ma, Ying Li, Jia-yuan Liu, Di Wu
Cluster science, emerged as a new research field in the 1960s, has attracted much attention because clusters represent a distinct state of matter and possess unique and tunable physicochemical properties as a function of size and geometry. The most significant advance in cluster science is that novel nano- or subnano-materials can be synthesised by assembling stable clusters and the properties of such materials can be tailored by adjusting size or composition of the cluster building blocks [1–8]. Another intriguing development in this field is the realisation that chosen stable clusters can mimic chemical property of single atoms in periodic table of elements [9–12]. Such clusters with well-defined size and composition have been termed superatoms in 1995 [13]. Since then, an increasing number of investigations have been performed to explore various superatoms, as well as study their structures, properties, and behaviour in compounds [9,11,14–23]. For example, the Al13 cluster was found to have similar chemical behaviour to a halogen atom [9], while Al14 has characteristics analogous to alkaline-earth metal in the Al14In− clusters [11].
Odd-even effect of the number of free valence electrons on the electronic structure properties of gold-thiolate clusters
Published in Molecular Physics, 2019
Yanle Li, Chunyan Liu, Vytor Oliveira, Dieter Cremer, Zijia Chen, Jing Ma
With the precise experimental structure, vast theoretical work focused on revealing the relationship between the topological structures and electronic structures. Häkkinen and coworkers introduced superatom complex (SAC) model to explain high stability of several spherical-like ligand-protected gold clusters [23]. The clusters with free valence electron number equal to that of the noble-gas were presumed to have higher stability. However, the SAC model did not work well for the clusters with non-spherical core. Later, supervalence bond (SVB) model was proposed and the non-spherical bi-icosahedral core of Au38(SR)24 could be viewed as a superatomic molecule. The core is an exact analogue of the covalent F2 molecule from the molecular orbital aspect [24]. Cheng et al. [25] also developed the superatom-network (SAN) to study the chemical bonding of electronically stable compounds Au18(SR)14, Au20(SR)16, and Au24(SR)20. Given that the valence electrons of the above clusters disobeyed the electron counts rule of the SAC model, the chemical bonding of these gold cores was revised as a network of n center-two electron, nc-2e (n = 2, 3, 4) superatom. Recently, Gao and coworkers developed a grand unified model (GUM) to describe the stability of a series of RS-AuNPs through an important principle that Au cores of the different sized RS-AuNPs can be built through the combination of elementary blocks such as triangular Au3(2e) and tetrahedral Au4(2e) [26].
C/N/O centred metal clusters: super valence bonding and magic structure with 26 valence electrons
Published in Molecular Physics, 2020
Jianling Tang, Cairong Zhang, Hongshan Chen
The physical and chemical properties of clusters differ from those of the bulk and exhibit strong dependence on size and composition. One of the most exciting developments in the field of clusters is that chosen cluster can mimic the chemical behaviours of a group of atoms in the periodic table. This idea offers the prospect of a new dimension of the periodic table formed by stable clusters called superatoms. And it offers the potential to create novel materials with tailored properties by using clusters as building units [1–4]. The electron counting rules are central to the understanding of superatoms, and they play an important part in designing these new species. The simplest electron counting rules are the octet rule and 18-electron rule; they correspond to the closed s2p6 and s2p6d10 electronic configurations of noble gas atoms. For simple metal clusters, the Jellium model is very successful in understanding their stabilities and properties [5–9]. This model assumes a uniform background of positive charge for the atomic nuclei and the core electrons, and the valence electrons from the individual atoms are treated nearly free and move in this potential. This leads to the Jellium shells of 1S21P61D102S21F142P6 … , and the shell closure gives the series of magic numbers 2, 8, 18, 20, 34, 40 … . (In this paper we use the uppercase S, P, D to denote the Jellium orbitals, and the lowercase s, p, d for atomic orbitals). The well-known example of Al13, with 39 valence electrons, needs one extra electron to close the 2P6 shells and behaves as a halogen atom [10–13]. While the Jellium model works very well for pure metal clusters, the scope of application of the Jellium model and modification of the theory to account for nonmetal doped metal clusters are still illusive.