On the Role of Alkali-Metal-Like Superatom Al12P in Reduction and Conversion of Carbon Dioxide

Developing efficient catalysts for the conversion of CO₂ into fuels and value-added chemicals is of great significance to relieve the growing energy crisis and global warming. With the assistance of DFT calculations, it was found that, different from Al₁₂X (X=Be, Al, and C), the alkali-metal-like superatom Al₁₂P prefers to combine with CO₂ via a bidentate double oxygen coordination, yielding a stable Al₁₂P(η²-O₂C) complex containing an activated radical anion of CO₂ (i.e., CO₂^.−). Thereby, this compound could not only participate in the subsequent cycloaddition reaction with propylene oxide but also initiate the radical reaction with hydrogen gas to form high-value chemicals, revealing that Al₁₂P can play an important role in catalyzing these conversion reactions. Considering that Al₁₂P has been produced in laboratory and is capable of absorbing visible light to drive the activation and transformation of CO₂, it is anticipated that this work could guide the discovery of additional superatom catalysts for CO₂ transformation and open up a new research field of superatom catalysis.     

Competition between halogen bond and hydrogen bond in complexes of superalkali Li3S and halogenated acetylene XCCH (X = F,Cl, Br,and I)

Complexes of superalkali Li₃S and XCCH (X = F, Cl, Br, and I) have been studied with theoretical calculations at the MP2/aug‐cc‐pVTZ level. Three types of structures are found: (A) the X atom combines with the S atom through a halogen bond; (B) the X atom interacts with the π electron of Li₃S by a π halogen bond; (C) the H atom combines with the S atom through a hydrogen bond. For A and B, a heavier halogen atom makes the interaction stronger, while for C, the change of interaction energy is not obvious, showing a small dependence on the nature of the X atom in HCCX. A is more stable than B and their difference in stability decreases as X varies from Cl to I. For the F and Cl complexes, A is weaker than C, however, the former is stronger than the latter in the Br and I complexes. The above three types of interactions have been analyzed by means of electron localization function, electron density difference, and energy decomposition, and the results show that they have similar nature and features with conventional interactions. © 2014 Wiley Periodicals, Inc.     

Tuning the electronic‐optical properties of porphyrin‐like porous C24N24 fullerene with (Li3O)n = (1–5) decoration. A computational study

Using DFT methods, the electronic properties and the first hyperpolarizabilities of porphyrin‐like porous C₂₄N₂₄ fullerene decorated with (Li₃O)_{n = (1–5)} have been systematically investigated. It is found that Li₃O molecules can effectively be adsorbed over N4 cavities of C₂₄N₂₄ with high interaction energies. This interaction is found to narrow the HOMO‐LUMO gap and work function values of C₂₄N₂₄. Thus its electronic properties are strongly sensitive to interaction with the Li₃O molecules. Indeed, compared with the sole parent C₂₄N₂₄ fullerene, (Li₃O)_{n = (1–5)}@C₂₄N₂₄ possess large first hyperpolarizabilities (β₀ ). Obviously, the Li₃O superalkali chemisorbed over C₂₄N₂₄ fullerene exhibit not only excellent stability but also large first hyperpolarizability. Therefore, they are expected to be potential innovative candidates for excellent electro‐optical materials.     

Alkalized borazine: A simple recipe to design closed‐shell superalkalis

Superalkalis are hypervalent species, possessing smaller ionization energy (IE) than alkali metal. These species are typically designed by electronegative atoms with excess electropositive ligands. Typical examples include FLi₂, OLi₃, NLi₄, etc. Herein, we study successive alkali metal substitution at H atoms in borazine (B₃N₃H₆). Our B3LYP and MP2 calculations demonstrate that the vertical ionization energy (VIE) of B₃N₃H_6‐xLi_x decreases with the increase in x for x = 1–6. For x ≥ 4, the VIE of B₃N₃H_6‐xLi_x becomes lower than that of Li atom, thereby indicating their superalkali nature. More interestingly, all these species are planar with closed‐shell structure such that the NICS_zz value at the ring's center is reduced. We have also studied B₃N₃M₆ (M = Li, Na, and K) species and found that the VIE is further reduced in case of Na and K substitutions. These findings should suggest a simple yet effective route to the design of species with lower ionization energies than alkali metal.     

Structural properties and nonlinear optical responses of superatom compounds BF4‐M (M = Li,FLi2, OLi3, NLi4)

A new type of superhalogen‐(super)alkali compound, BF₄‐M (M = Li, FLi₂, OLi₃, NLi₄), is theoretically characterized at the MP2/6‐311+G(3df) level. The interaction between superhalogen BF₄ and different shaped (super)alkali M is found to be strong and ionic in nature. Bond energies of these BF₄‐M species are in the range of 200.0–226.7 kcal/mol at the CCSD(T)/6‐311+G(3df) level, which are much larger than the traditional ionic bond energy of 130.1 kcal/mol of FLi. In addition, different from the alkali halides, the BF₄‐M compounds prefer to dissociate into ions rather than neutral fragments. The energetic properties of BF₄‐M are found to be closely related to the size of the M subunit. The different effects of superalkali and superhalogen subunits on the nonlinear optical (NLO) properties of such superatom compounds are also revealed. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

平面星形CBe5Li5+超碱离子团簇的结构及其储氢性能研究

采用密度泛函理论(DFT)方法,研究平面星形CBe5Li5+超碱离子团簇的结构及其储氢性能。结果表明, 平面星形D5h结构的CBe5Li5+超碱离子团簇具有较高的热力学稳定性,氢分子能在Li+周围发生吸附, 且每个Li+周围能有效吸附三个氢分子。结构的稳定性及合适的吸氢性能表明平面星形CBe5Li5+超碱离子团簇在常温常压条件下可以作为较好的储氢媒介。     

Record Low Ionization Potentials of Alkali Metal Complexes with Crown Ethers and Cryptands

Electronic properties of series of alkali metals complexes with crown ethers and cryptands were studied via DFT hybrid functionals. For [M([2.2.2]crypt)] (M=Li, Na, K) extremely low (1.70–1.52 eV) adiabatic ionization potentials were found. Such low values of ionization energies are significantly lower than those of alkali metal atoms. Thus, the investigated complexes can be defined as superalkalis. As a result, our investigation opens up new directions in the designing of chemical species with record low ionization potentials and extends the explanation of the ability of the cryptates and alkali crown ether complexes to stabilize multiple charged Zintl ions.     

Recent Progress on the Design,Characterization, and Application of Superalkalis

Superalkalis are clusters or molecules featuring lower ionization energies (IEs) than that of cesium atoms, and thus exhibit excellent reducing properties. Such special species have great potential to be used in the synthesis of unusual charge-transfer salts and cluster-assembled nanomaterials with tailored properties, in the reduction of carbon dioxide, or as hydrogen storage materials and noble-gas-trapping agents, etc. In this regard, ongoing efforts have been devoted to designing and characterizing superalkalis of new types. The recent progress on the study of superalkalis in terms of theoretical design, characterization, and potential application is summarized in this minireview. We hope this review will not only provide a broad overview of this research field, but also highlight the prospect of further extending the experimental synthesis and practical application of superalkalis.