Simple and scalable synthesis of the carborane anion CB11H12. Dalton Trans 2019;48:7499-7502. [PMID: 30912562 DOI: 10.1039/c9dt01062a]

Electrolyte Engineering with Carboranes for Next-Generation Mg Batteries

To realize an energy storage transition beyond Li-ion competitive technologies, earth-abundant elements, such as Mg, are needed. Carborane anions are particularly well-suited to realizing magnesium-ion batteries (MIBs), as their inert and weakly coordinating properties beget excellent electrolyte performance. However, utilizing these materials in actual electrochemical cells has been hampered by the reliance on the Mg2+ salts of the commercially available [HCB11H11]- anion, which is not soluble in more weakly binding solvents apart from the higher glymes. Herein, we demonstrate it is possible to iteratively engineer the [HCB11H11]- anion surface synthetically to address previous solubility issues and yield a highly conductive (up to 7.33 mS cm-1) and electrochemically stable (up to +4.2 V vs Mg2+/0) magnesium electrolyte that surpasses the state of the art. This novel non-nucleophilic electrolyte exhibits highly dissociative behavior regardless of concentration and is tolerant of prolonged periods of cycling in symmetric cells at high current densities (up to 2.0 mA cm-2, 400 h). The hydrocarbon functionalized carborane electrolyte presented here demonstrates >96% Coulombic efficiency when paired with a Mo6S8 cathode. This approach realizes a needed candidate to discover next-generation cathode materials that can enable the design of practical and commercially viable Mg batteries.

Divalent closo-monocarborane solvates for solid-state ionic conductors

Li-ion batteries have held the dominant position in battery research for the last 30+ years. However, due to inadequate resources and the cost of necessary elements (e.g., lithium ore) in addition to safety issues concerning the components and construction, it has become more important to look at alternative technologies. Multivalent metal batteries with solid-state electrolytes are a potential option for future battery applications. The synthesis and characterisation of divalent hydrated closo-monocarborane salts - Mg[CB₁₁H₁₂]₂·xH₂O, Ca[CB₁₁H₁₂]₂·xH₂O, and Zn[CB₁₁H₁₂]₂·xH₂O - have shown potential as solid-state electrolytes. The coordination of a solvent (e.g. H₂O) to the cation in these complexes shows a significant improvement in ionic conductivity, i.e. for Zn[CB₁₁H₁₂]₂·xH₂O dried at 100 °C (10^-3 S cm^-1 at 170 °C) and dried at 150 °C (10^-5 S cm^-1 at 170 °C). Solvent choice also proved important with the ionic conductivity of Mg[CB₁₁H₁₂]₂·3en (en = ethylenediamine) being higher than that of Mg[CB₁₁H₁₂]₂·3.1H₂O (2.6 × 10^-5 S cm^-1 and 1.7 × 10^-8 S cm^-1 at 100 °C, respectively), however, the oxidative stability was lower (<1 V (Mg²⁺/Mg) and 1.9 V (Mg²⁺/Mg), respectively). Thermal characterisation of the divalent closo-monocarborane salts showed melting and desolvation, prior to high temperature decomposition.

Zinc Ammonio-dodecaborates: Synthesis, Lewis Acid Strength, and Reactivity

Two series of zinc salts, [EtZn][A] and Zn[A]₂, with weakly coordinating anions [A]^- as counterions have been prepared, and their activities as catalysts for hydrosilylation reactions of 1-hexene, benzophenone, and acetophenone have been investigated. The counterions and per- and partially chlorinated 1-ammonio-closo-dodecaborate anions [Me₃NB₁₂Cl₁₁]^- [1]^-, [Pr₃NB₁₂H₅Cl₆]^- [2]^-, [Bu₃NB₁₂H₄Cl₇]^- [3]^-, and [Hex₃NB₁₂H₅Cl₆]^- [4]^- were chosen as potential and more readily available alternatives to carborate anions such as [CHB₁₁Cl₁₁]^- and [HexCB₁₁Cl₁₁]^-. The basicity of anion [4]^- was determined as being close to that of the triflimide anion [N(SO₂CF₃)₂]^-, and the fluoride ion affinities (FIAs) of compounds [EtZn][2] and Zn[2]₂ are lower than those of the Lewis acids B(C₆F₅)₃ and Zn[HexCB₁₁Cl₁₁]₂. The higher anion basicity and the resulting lower Lewis acidity of the zinc centers result in low activity in 1-hexene hydrosilylation catalysis and only moderate activity in the hydrosilylation catalysis of benzophenone and acetophenone.

Synthesis of closo-CB11H12- Salts Using Common Laboratory Reagents

Lithium and sodium salts of the closo-carbadodecaborate anion [CB₁₁H₁₂]^- have been shown to form stable solid-state electrolytes with excellent ionic conductivity for all-solid-state batteries (ASSB). However, potential commercial application is currently hindered by the difficult, low-yielding, and expensive synthetic pathways. We report a novel and cost-effective method to synthesize the [CB₁₁H₁₂]^- anion in a 40% yield from [B₁₁H₁₄]^-, which can be synthesized using common laboratory reagents. The method avoids the use of expensive and dangerous reagents such as NaH, decaborane, and CF₃SiMe₃ and shows excellent reproducibility in product yield and purity.

Monocarborane cluster as a stable fluorine-free calcium battery electrolyte

High-energy-density and low-cost calcium (Ca) batteries have been proposed as ‘beyond-Li-ion’ electrochemical energy storage devices. However, they have seen limited progress due to challenges associated with developing electrolytes showing reductive/oxidative stabilities and high ionic conductivities. This paper describes a calcium monocarborane cluster salt in a mixed solvent as a Ca-battery electrolyte with high anodic stability (up to 4 V vs. Ca²⁺/Ca), high ionic conductivity (4 mS cm⁻¹), and high Coulombic efficiency for Ca plating/stripping at room temperature. The developed electrolyte is a promising candidate for use in room-temperature rechargeable Ca batteries.

Unprecedented icosahedral clusters built of polyantimony: from single [Ni0.5@{Sb6Ni6(CO)8}]4− and [Ni@{Sb7Ni5(CO)6}]3− to the Sb84−-linked dimer [(Sb8){Sb7Ni5(CO)4}2]6−

First icosahedral clusters built of polyantimony were prepared from the reactions of K2ZnSb and Ni(CO)2(PPh3)2. Sb84−-linked dimer provides a new way of thinking for the synthesis of hybrid clusters datively coordinated by polydentate Zintl anions.

Building blocks for the chemistry of perfluorinated alkoxyaluminates [Al{OC(CF3)3}4]-: simplified preparation and characterization of Li+-Cs+, Ag+, NH4+, N2H5+ and N2H7+ salts

Advanced weakly coordinating anions (WCAs) significantly facilitate synthesis of various exotic chemical compounds and novel, potentially useful materials. One of such anions - [Al{OC(CF₃)₃}₄]^-, denoted [Al(OR^F)₄]^-, appears particularly convenient, as it can be easily prepared from the commercially available alanates and HOC(CF₃)₃. Here we present a thorough characterization of a series of solvent-free M[Al(OR^F)₄] salts, M = Li-Cs, Ag, NH₄, N₂H₅ and N₂H₇, and related compounds of monovalent cations, which are crucial starting materials for further work with these species. Notably, the corresponding synthetic protocols are updated by an improved method for fast, facile and easily scalable synthesis of Li[Al(OR^F)₄], which remains the most useful primary source of the anion. The physico-chemical properties of these salts including crystal structures, thermal stability by TG/DSC, vibrational spectra as well as solubility are discussed in a systematic fashion.

Insertion of Carbenes into Deprotonated nido-Undecaborane, B11H13(2-)

We have examined the insertion of carbenes carrying leaving groups into the [nido-B11H13]2- dianion to form the [closo-1-CB11H12]- anion. The best procedure uses CF3SiMe3 and LiCl as the source of CF2. It is simple, convenient and scalable and proceeds with 70-90% yield. Density functional calculations have been used to develop a mechanistic proposal that accounts for the different behavior of CF2, requiring only one equivalent of base for successful conversion of Na[nido-B11H14]- to [closo-1-CB11H12]-, and CCl2 and CBr2, which require more.