Magnesium-Based Oxyfluoride Superatoms: Design, Structure, and Electronic Properties

Tuning the electronic structure of gold cluster-assembled materials by altering organophosphine ligands

Superatomic clusters can be assembled to build bulk matter, where the individual characteristics are preserved. The main benefit of these materials over conventional bulk species is the capability to tailor their features by altering the physicochemical identities of individual clusters. Electronic properties of metal clusters can be modified by a protective shell of ligands that attach to the surface and make the whole nanoparticle soluble in organic or aqueous solvents. In the present work, we demonstrate that properly chosen ligands provide not only steric protection from aggregation but also tune the redox activity of metal clusters. We investigate the role of the ligands in electronic structure tunability and ligand-field splitting. Our first-principles calculations agree with the experiments, showing that phosphine-protected gold materials are small gap semiconductors. The obtained bandgaps strongly depend on the ligand used. Hence, using phosphine and organophosphine ligands should be feasible and promising while designing the novel superatom-based materials since the desired range of the bandgap might be achieved (by the proper choice of the ligand).

Design and Investigation of Superatoms for Redox Applications: First-Principles Studies

A superatom is a cluster of atoms that acts like a single atom. Two main groups of superatoms are superalkalis and superhalogens, which mimic the chemistry of alkali and halogen atoms, respectively. The ionization energies of superalkalis are smaller than those of alkalis (<3.89 eV for cesium atom), and the electron affinities of superhalogens are larger than that of halogens (>3.61 eV for chlorine atom). Exploring new superalkali/superhalogen aims to provide reliable data and predictions of the use of such compounds as redox agents in the reduction/oxidation of counterpart systems, as well as the role they can play more generally in materials science. The low ionization energies of superalkalis make them candidates for catalysts for CO2 conversion into renewable fuels and value-added chemicals. The large electron affinity of superhalogens makes them strong oxidizing agents for bonding and removing toxic molecules from the environment. By using the superatoms as building blocks of cluster-assembled materials, we can achieve the functional features of atom-based materials (like conductivity or catalytic potential) while having more flexibility to achieve higher performance. This feature paper covers the issues of designing such compounds and demonstrates how modifications of the superatoms (superhalogens and superalkalis) allow for the tuning of the electronic structure and might be used to create unique functional materials. The designed superatoms can form stable perovskites for solar cells, electrolytes for Li-ion batteries of electric vehicles, superatomic solids, and semiconducting materials. The designed superatoms and their redox potential evaluation could help experimentalists create new materials for use in fields such as energy storage and climate change.

Modified Lennard-Jones potentials for nanoscale atoms

A classical 6-12 Lennard-Jones (LJ) equation has been widely used to model materials and is the potential of choice in studies when the focus is on fundamental issues. Here we report a systematic study comparing the pair interaction potentials within solid-state materials (i.e., [Co₆ Se₈ (PEt₃ )₆ ][C₆₀ ]₂ , [Cr₆ Te₈ (PEt₃ )₆ ][C₆₀ ]₂ , [Ni₉ Te₆ (PEt₃ )₈ ][C₆₀ ]) using density functional theory (DFT) calculations and LJ parametrization. Both classical (6-12 LJ) and modified LJ (mLJ) models were developed. In the mLJ approach, the exponents 6 and 12 are replaced by different integer number n and 2n, respectively, and an additional parameter (α) is introduced to describe intermolecular distance shift arising within the geometric centers' approach (instead of the shortest interatomic distance between particles). A general LJ approach reexamination reveals that in the case of nanoatoms, the attractive term decays with distance as the inverse fourth power, and the dominating at short distances repulsive term decays as the inverse eighth power. The modification of the LJ equation is even more prominent for interaction profiles, where intermolecular distance corresponds to separation between geometric centers of particles. In this approach, the attractive term decays with distance as the inverse 12th power, while the repulsive term decays rapidly (as the inverse 24th power). Thus, the mLJ models (e.g., 4-8 LJ) rather than the 6-12 classical ones seem to be a better choice for the description of binary interactions of nanoatoms. The developed mLJ models and electronic structure characteristics give an insight into the explanation of the unique physicochemical properties of superatomic-based solid-state materials.

Magnesium-Based Clusters as Building Blocks of Electrolytes in Lithium-Ion Batteries

Superhalogens, owing to their large electron affinity (EA, exceeding those of any halogen atom), play an essential role in physical chemistry as well as new material design. They have applications in hydrogen storage and lithium-ion batteries. Owing to the unique geometries and electronic features of magnesium-based clusters, their potential to form a new class of lithium salts has been investigated here theoretically. The idea is assessed by conducting ab initio computations on Li⁺ /Mg_n F_2n+1-2m O_m ^- compounds (n=2, 3; m=0-3) and analyzing their performance as potential Li-ion battery electrolytes. The Mg₃ F₇ ^- cluster, with large electron binding energy (EA of 7.93 eV), has been proven to serve as a building block for lithium salts. It is shown that, apart from high electronic stability, the new superhalogen-based electrolytes exhibit a set of desirable properties, including a large band gap, high electrolyte stability window, easy mobility of the Li⁺ , and favorable insensitivity to water.