Superhalogens: A Bridge between Complex Metal Hydrides and Li Ion Batteries

The catalytic performance of (ZrO)n (n = 1-4, 12) clusters for Suzuki-Miyaura cross-coupling: a DFT study

Superatoms are special clusters with similar physicochemical properties to individual atoms in the periodic table, which open up new avenues for exploring inexpensive catalysts. Given that the ZrO superatom possesses the same number of valence electrons as a Pd atom, the mechanisms of the Suzuki-Miyaura reaction catalyzed by (ZrO)n (n = 1-4) clusters have been investigated and compared with the corresponding Pdn (n = 1-4) species to explore superatom-based catalysts for the formation of C-C bonds via a density functional theory (DFT) study. It was interesting to find that the catalytic activities of (ZrO)n (n = 1-4) towards the Suzuki-Miyaura reaction gradually improved as the cluster size increased. Therefore, to obtain more efficient catalysts, the catalytic activity of a well-designed (ZrO)12 nanocage towards this cross-coupling reaction has been further evaluated. Gratifyingly, this nanocage shows excellent catalytic performance for the considered coupling reaction, which is even comparable to that of the commonly used Pd catalyst and outperforms the corresponding Pd12 cluster. We hope this study can not only provide valuable guidance for the development of noble metal-like catalysts for C-C bond formation, but also expand the application of superatoms in the catalysis of organic reactions.

Strongly Bound Polynuclear Anions Comprising Scandium Fluoride Building Blocks

The stability of polynuclear anions composed of ScF3 building blocks was studied by using ab initio and density functional theory electronic structure methods and flexible basis sets. Thorough exploration of ground state potential energy surfaces of (Sc2F7)-, (Sc3F10)-, and (Sc4F13)- anions which may be viewed as comprising ScF3 fragments and the additional fluorine atom led to determining the isomeric structures thereof. It was found that the most stable isomers which are predicted to dominate at room temperature correspond to the compact structures enabling the formation of a large number of Sc-F-Sc bridging linkages rather than to the chain-like structures. The vertical electron detachment energies of the (ScnF3n+1)- anions were found to be very large (spanning the 10.85-12.29 eV range) and increasing with the increasing number of scandium atoms (n) and thus the ScF3 building blocks involved in the structure. Thermodynamic stability of (ScnF3n+1)- anions (i.e., their susceptibility to fragmentation) was also verified and discussed.

Colossal Stability of SiB11 (BO)12 - : An Implication as Potential Electrolyte in High-Voltage Alkali-ion Battery

High-voltage alkali metal-ion batteries (AMIBs) require a non-hazardous, low-cost, and highly stable electrolyte with a large operating potential and rapid ion conductivity. Here, we have reported a halogen-free high-voltage electrolyte based on SiB11 (BO)12 - . Because of the weak π-orbital interaction of -BO as well as the mixed covalent and ionic interaction between SiB11 -cage and -BO ligand, SiB11 (BO)12 - has colossal stability. SiB11 (BO)12 - possesses extremely high vertical detachment energy (9.95 eV), anodic voltage limit (∼10.05 V), and electrochemical stability window (∼9.95 V). Furthermore, SiB11 (BO)12 - is thermodynamically stable at high temperatures, and its large size allows for faster cation movement. The alkali salts MSiB11 (BO)12 (M=Li, Na, and K) are easily dissociated into ionic components. Electrolytes based on SiB11 (BO)12 - greatly outperform commercial electrolytes. In short, SiB11 (BO)12 - -based compound is demonstrated to be a high-voltage electrolyte for AMIBs.

Influence of Solvent System on the Electrochemical Properties of a closo-Borate Electrolyte Salt

In this study, the use of a closo-borate salt as an electrolyte for lithium-ion batteries (LIB) was evaluated in a series of solvent systems. The lithium closo-borate salts are a unique class of halogen-free salts that have the potential to offer some advantages over the halogenated salts currently employed in commercially available LIB due to their chemical and thermal stability. To evaluate this concept, three different solvent systems were prepared with a lithium closo-borate salt to make a liquid electrolyte (propylene carbonate, ethylene carbonate:dimethyl carbonate, and 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide). The closo-borate containing electrolytes were then compared by utilizing them with three different electroactive electrode materials. Their cycle stability and performance at various charge/discharge rates was also investigated. Based on the symmetrical cell and galvanostaic cycling studies it was determined that the carbonate based liquid electrolytes performed better than the ionic liquid electrolyte. This work demonstrates that halogen free closo-borate salts are interesting candidates and worthy of further investigation as lithium salts for LIB.

Tripodal Podand Ligand with a Superhalogen Nature as an Effective Molecular Trap

Tris(2-methoxyethyl) fluoroborate anion (TMEFA), anovel tripodal ligand based on the BF4− superhalogen anion, is proposed and was investigated theoretically using ab initio MP2 (second-order Møller-Plesset perturbational method) and OVGF (outer valence Green function) methods. The studied molecule comprises three 2-methoxyethoxy groups (-O-CH2-CH2-O-CH3) connected to a central boron atom, which results in the C3-symmetry of the compound. The resulting anion was stable against fragmentation processes and its vertical electron detachment energy was found to be 5.72 eV. Due to its equilibrium structure resembling that of classical tripodal podands, the [F-B(O-CH2-CH2-O-CH3)3]− anion is capable of binding metal cations using its three arms, and thus may form strongly bound ionic complexes such as [F-B(O-CH2-CH2-O-CH3)3]−/Li+ and [F-B(O-CH2-CH2-O-CH3)3]−/Mg2+. The binding energies predicted for such compounds far exceed those of the similar neutral classical podand ligands, which likely makes the [F-B(O-CH2-CH2-O-CH3)3]− system a more effective molecular trap or steric shielding agent with respect to selected metal cations.

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

The ability of mixed ligands to form stable dinuclear and trinuclear magnesium-based superatoms has been investigated theoretically. The Mg₂F_{5-2 m}O _m and Mg₃F_{7-2 m}O _m systems (where m = 1-3) were found able to form stable and strongly bound anionic clusters, and those assumptions were validated by (i) the analysis of the geometrical stability; (ii) the estimated Gibbs free energies for the most probable disproportion paths these clusters might be vulnerable to (which allows examining their thermodynamic stabilities); (iii) the localization of the electron density; and (iv) the adiabatic electron affinity (AEA), vertical electron detachment energy (VDE), and adiabatic electron detachment energy (ADE) values calculated for the studied systems. It is demonstrated that the stability of the anionic daughters of these clusters increases with the number of electronegative ligands, and Mg _nF_{2 n+1-2 m}O _m^- ( n = 2, 3; m = 1-3) clusters are stable against electron emission. The largest electron binding energy was found for the Mg₃F₅O^- anion (VDE = 6.826 eV). The strong VDE dependence on (i) the geometrical structure, (ii) the number of central atoms, (iii) ligand type, and (iv) bonding/antibonding character of the highest molecular orbital (HOMO) was also remarked upon and discussed.

Theoretical Study of Halogenated B12H nX(12- n)2- (X = F, Cl, Br)

The closoborane and their derivatives have attracted high interest due to their superionic conductivity. Very recently, high ionic conductivities have been reported for compounds containing the closoborane ion B₁₂H₁₂^2-. In this work, we address halogen-substituted ions B₁₂H _nX_{(12- n)}^2- ( n = 0-3, 6, 9-12 and X = F, Cl, Br) using DFT calculations to probe the structures, the chemical stability, and the electrochemical stability, as well as spectroscopic properties in view of potential future applications. Considering the theoretical reaction n/12 B₁₂H₁₂^2- + (12- n)/12 B₁₂X₁₂^2- → B₁₂H _nX_{(12- n)}^2-, it appears that for X = Cl and Br the compounds with n = 6 are stabilized by about 100 kJ/mol. The calculation of the vertical detachment energy (which is indirectly related to the electrochemical stability) shows an increasing stability with increasing halogen content. These results suggest that, for practical applications, it is likely that a partially halogenated ion offers the best compromise. The calculations of vibrational properties and NMR chemical shifts also reveal several systematic trends, which are discussed and compared to available literature values.

A theoretical study on the structures and electronic and magnetic properties of new boron nitride composite nanosystems by depositing superhalogen Al13 on the surface of nanosheets/nanoribbons

Inorganic boron nitride (BN) nanomaterials possess outstanding physical and chemical characteristics, and can be considered as an excellent building block to construct new composite nanomaterials. In this work, on the basis of the first-principles computations, a new type of composite nanostructure can be constructed by depositing superhalogen Al13 on the surface of low-dimensional BN monolayer or nanoribbons (BNML/BNNRs). All these Al13-modified BN nanosystems can possess large adsorption energies, indicating that superhalogen Al13 can be stably adsorbed on the surface of these BN materials. In particular, it is revealed that independent of the chirality, ribbon width and adsorption site, introducing superhalogen Al13 can endow the BN-based composite systems with a magnetic ground state with a magnetic moment of about 1.00 μB, and effectively narrow their robust wide band gaps. These new superhalogen-Al13@BN composite nanostructures, with magnetism and an appropriate band gap, can be very promising to be applied in multifunctional nanodevices in the near future.

Adsorbing the magnetic superhalogen MnCl3 to realize intriguing half-metallic and spin-gapless-semiconducting behavior in zigzag or armchair SiC nanoribbon

By means of first-principles computations, we first propose a new and effective strategy through adsorbing the magnetic superhalogen MnCl3 to modulate the electronic and magnetic properties of zigzag- and armchair-edged SiC nanoribbons (zSiCNR and aSiCNR, respectively). In view of its large intrinsic magnetic moment and strong electron-withdrawing ability, the adsorption of magnetic superhalogen MnCl3 can introduce magnetism in the substrate SiCNR, and simultaneously induce the electron transfer process from SiCNR to MnCl3, resulting in the evident increase of electrostatic potential in the ribbon plane, like applying an electric field. As a result, the magnetic degeneracy of pristine zSiCNR can be broken and a robust ferromagnetic half-metallicity or metallicity can be observed in the modified zSiCNR systems, while a robust ferromagnetic half-metallic or spin-gapless-semiconducting behavior can be obtained in the modified aSiCNR systems. Note that both the appealing half-metallicity and spin-gapless-semiconductor behavior are key features which hold promise for future spintronic applications. Moreover, all of these new superhalogen-SiC nanosystems can possess considerably high structural stabilities. These intriguing findings will be advantageous for promoting excellent SiC-based nanomaterials in the applications of spintronics and multifunctional nanodevices in the near future.

Design of superhalogens using a core-shell structure model

Superhalogens, which have larger electron affinity than any halogen, play an important role in physical chemistry and materials design because of their applications in hydrogen storage and lithium-ion batteries. Inspired by the unique geometries and electronic properties of II-VI/III-V cage clusters, particularly the experimentally synthesized B₁₂N₁₂, we propose a core-shell structure model to design new superhalogens. The idea is assessed by conducting ab initio calculations on endohedral cage clusters X@B₁₂N₁₂ (X = F, Cl, Br) and other similar systems. With an exceptionally large electron affinity of 5.36 eV, the stable F@B₁₂N₁₂ cluster behaves as a novel superhalogen that can serve as a building block for Li salts and hyperhalogens. The findings highlight a new route for the discovery of superhalogens and provide useful building blocks for the bottom-up design of materials.

Does the endohedral borospherene supersalt FLi2@B39maintain the “super” properties of its subunits?

The behavior of the entirely unique system represented by superalkaline species incorporated into a superhalogen cage has been studied using density functional theory. The calculations revealed that superhalogen and superalkaline properties inherent in the separated fragments are lost in FLi₂@B₃₉complexes.

Could the increased structural versatility imposed by non-halogen ligands bring something new for polynuclear superhalogens? A case study on binuclear [Mg2L5]− (L = –OH, –OOH and –OF) anions

A combined ab initio and DFT study is performed in this work to explore the superhalogen properties of polynuclear structures based on the ligands of –OH, –OOH and –OF.

Oxidizing CO2 with superhalogens

The Sb₃F₁₆ species was found to be capable of ionizing the CO₂ molecule.

Role of ligands in the stability of BnXn and CBn−1Xn (n = 5–10; X = H, F, CN) and their potential as building blocks of electrolytes in lithium ion batteries

We predict a series of boron-cage-based stable (di-)anions, and demonstrate them to be high-performance electrolytes in Li-ion batteries.

Organo-Zintl Clusters [P7R4]: A New Class of Superalkalis

Zintl ions composed of Group 13, 14, and 15 elements are multiply charged cluster anions that form the building blocks of the Zintl phase. Superalkalis, on the other hand, are cationic clusters that mimic the chemistry of the alkali atoms. It is, therefore, counterintuitive to expect that Zintl anions can be used as a core to construct superalkalis. In this paper, using density functional theory, we show that this is indeed possible. The results are compared with calculations at the MP2 level of theory. A systematic study of a P7(3-) Zintl core decorated with organic ligands [R = Me, CH2Me, CH(Me)2 and C(Me)3] shows that the ionization energies of some of the P7R4 species are smaller than those of the alkali atoms and hence can be classified as superalkalis. This opens the door to the design and synthesis of a new class of superalkali moieties apart from the traditional ones composed of only inorganic elements.

Superhalogen properties of BS2(-) and BSO(-): photoelectron spectroscopy and theoretical calculations

We investigate BS2(-) and BSO(-) clusters using photoelectron spectroscopy and theoretical calculations. The electron affinities of BS2 and BSO are measured to be 3.80 ± 0.03 and 3.88 ± 0.03 eV, respectively, higher than those of halogen atoms. Thus, BS2 and BSO can be considered as superhalogens. The comparison of experimental and theoretical results confirmed that the ground state structures of BS2(-), BSO(-), and their neutrals are all linear. Analyses of natural bond orbitals suggest that both BS2(-) and BSO(-) have dual 3c-4e π hyperbonds.

Probing the potential of halogen-free superhalogen anions as effective electrolytes of Li-ion batteries: a theoretical prospect from combined ab initio and DFT studies

The potential of superhalogens as efficient components of electrolytes in Li-ion batteries is verified from ab initio and DFT studies.