Some neural or partially oxidized metal ammonia complexes mimic alkali-metals and alkaline-earth metals, hence, can be recognized as “superatoms”. For example, M(NH3)4 (M = Li and Na) bear one electron in a quasi-spherical atomic s-type orbital (or superatomic 1s-orbital) and mimic alkali-metals (see 1s orbital of Figure). On the other hand, M(NH3)4 (M = Be and Mg) mimic alkaline-earth metals owing to the doubly occupied superatomic 1s-orbital. Fascinatingly, these superatoms populate higher angular momentum p-, d-, f-, and g-type orbitals in low-lying excited electronic states. We have benchmarked a series of basis sets comparing with experimental excitation energies and electron affinities and found that the use of augmented basis functions on atoms is extremely important especially for precise representation of their low-lying electronic states. Considering the orbital contours and the excitation energies we introduced their “Superatomic Aufbau principle” which reads as 1s, 1p, 1d, 2s, 2p, 1f, 2d, 3s, and 1g. These superatoms can bind together to create stable aggregates. The geometry of such a system is governed by two factors: (1) correct description of H-bonding interactions and (2) accurate representation of the diffuse electron. We have benchmarked a series of density functionals against golden standard CCSD(T) results and found that CAM-B3LYP can accurately describe structures of such clusters. Aggregates of these superatoms produce a sea-of-electrons in the periphery and become stabilized. Furthermore, their electronic structures and chemical and physical properties will be discussed.

Ground and excited electronic structures of metal-ammonia superatoms and how to design novel 2D- and 3D-materials from them

ACS Fall 2021

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