Comparison of the Coordination of B12F122–, B12Cl122–, and B12H122– to Na+ in the Solid State: Crystal Structures and Thermal Behavior of Na2(B12F12), Na2(H2O)4(B12F12), Na2(B12Cl12), and Na2(H2O)6(B12Cl12)

Closo-Borate Gel Polymer Electrolyte with Remarkable Electrochemical Stability and a Wide Operating Temperature Window

A major challenge in the pursuit of higher-energy-density lithium batteries for carbon-neutral-mobility is electrolyte compatibility with a lithium metal electrode. This study demonstrates the robust and stable nature of a closo-borate based gel polymer electrolyte (GPE), which enables outstanding electrochemical stability and capacity retention upon extensive cycling. The GPE developed herein has an ionic conductivity of 7.3 × 10^-4  S cm^-2 at room temperature and stability over a wide temperature range from -35 to 80 °C with a high lithium transference number ( tLi+$t_{{\rm{Li}}}^ + $ = 0.51). Multinuclear nuclear magnetic resonance and Fourier transform infrared are used to understand the solvation environment and interaction between the GPE components. Density functional theory calculations are leveraged to gain additional insight into the coordination environment and support spectroscopic interpretations. The GPE is also established to be a suitable electrolyte for extended cycling with four different active electrode materials when paired with a lithium metal electrode. The GPE can also be incorporated into a flexible battery that is capable of being cut and still functional. The incorporation of a closo-borate into a gel polymer matrix represents a new direction for enhancing the electrochemical and physical properties of this class of materials.

KNa0.78Eu0.27In3.80B12S12: A Novel Hexanary Thioborate Featuring B12S12 Cluster and Diverse InSx (x = 4, 5, 6) Units

Thioborates combine the advantages of sulfides and borates, are a new type of multifunctional inorganic materials with versatile structural features. Here, a thioborate KNa0.78Eu0.27In3.80B12S12 crystallizing with a new structure-type was...

KEu2In3B12S13: A Novel Type of Thioborate Featuring B12S12 Cluster and Unique In6S6 12-membered Ring

Both borates and sulfides are important inorganic multifunctional materials. Encouraged by this background, thioborates attract broad interest. However, their investigations are highly hindered by the available ones’ scarcity and new...

Synthesis and structural properties of a 2D Zn(II) dodecahydroxy-closo-dodecaborate coordination polymer

In this work, we discuss the synthesis and characterization of a 2D coordination polymer composed of a dianionic perhydroxylated boron cluster, [B12(OH)12]2-, coordinated to Zn(II)—the first example of a transition...

Boron Hydrogen Compounds: Hydrogen Storage and Battery Applications

About 25 years ago, Bogdanovic and Schwickardi (B. Bogdanovic, M. Schwickardi: J. Alloys Compd. 1-9, 253 (1997) discovered the catalyzed release of hydrogen from NaAlH4. This discovery stimulated a vast research effort on light hydrides as hydrogen storage materials, in particular boron hydrogen compounds. Mg(BH4)2, with a hydrogen content of 14.9 wt %, has been extensively studied, and recent results shed new light on intermediate species formed during dehydrogenation. The chemistry of B3H8-, which is an important intermediate between BH4- and B12H122-, is presented in detail. The discovery of high ionic conductivity in the high-temperature phases of LiBH4 and Na2B12H12 opened a new research direction. The high chemical and electrochemical stability of closo-hydroborates has stimulated new research for their applications in batteries. Very recently, an all-solid-state 4 V Na battery prototype using a Na4(CB11H12)2(B12H12) solid electrolyte has been demonstrated. In this review, we present the current knowledge of possible reaction pathways involved in the successive hydrogen release reactions from BH4- to B12H122-, and a discussion of relevant necessary properties for high-ionic-conduction materials.

Strong Binding of Noble Gases to [B12X11]-: A Theoretical Study

We systematically explore the stability and properties of [B₁₂X₁₁NG]^- adducts resulting from the binding of noble gas atoms to anionic [B₁₂X₁₁]^- clusters in the gas phase of mass spectrometers. [B₁₂X₁₁]^- can be obtained by stripping one X^- off the icosahedral closo-dodecaborate dianion [B₁₂X₁₂]^2-. We study the binding of the noble gas atoms He, Ne, Ar, Kr, and Xe to [B₁₂X₁₁]^- with substituents X = F, Cl, Br, I, and CN. While He cannot be captured by these clusters and Ne only binds at low temperatures, the complexes with the heavier noble gas atoms Ar, Kr, and Xe show appreciable complexation energies and exceed 1 eV at room temperature in the case of [B₁₂(CN)₁₁Xe]^-. The predicted B-NG equilibrium distance in the complexes with Ar, Kr, and Xe is only 0.10-0.25 Å longer than the sum of the covalent radii of the two corresponding atoms, and a significant charge transfer from the noble gas atom to the icosahedral B₁₂ cage is observed.

Iodine-Substituted Lithium/Sodium closo-Decaborates: Syntheses, Characterization, and Solid-State Ionic Conductivity

Solid-state electrolytes based on closo-decaborates have caught increasing interest owing to the impressive room-temperature ionic conductivity, remarkable thermal/chemical stability, and excellent deformability. In order to develop new solid-state ion conductors, we investigated the influence of iodine substitution on the thermal, structural, and ionic conduction properties of closo-decaborates. A series of iodinated closo-decaborates, M₂[B₁₀H_10-nI_n] (M = Li, Na; n = 1, 2, 10), were synthesized and characterized by thermal analysis, powder X-ray diffraction, and electrochemical impedance spectroscopy; the stability and ionic conductivity of these compounds were studied. It was found that with the increase of iodine substitution on the closo-decaborate anion cage, the thermal decomposition temperature increases. All M₂[B₁₀H_10-nI_n] exhibit an amorphous structure. The ionic conductivity of Li₂[B₁₀H_10-nI_n] is higher than that of the Li₂[B₁₀H₁₀] parent compound. An ionic conductivity of 2.96 × 10^-2 S cm^-1 with an activation energy of 0.23 eV was observed for Li₂[B₁₀I₁₀] at 300 °C, implying that iodine substitution can improve the ionic conductivity. However, the ionic conductivity of Na₂[B₁₀H_10-nI_n] is lower than that of Na₂[B₁₀H₁₀] and increases with the increase of iodine substitution, which could be associated with the increase of the electrostatic potential, mass, and volume of the iodinated anions. Moreover, Li₂[B₁₀I₁₀] offers a Li-ion transference number of 0.999, an electrochemical stability window of 3.3 V and good compatibility with the Li anode, demonstrating its potential for application in high-temperature batteries.

Structural and Dynamical Properties of Potassium Dodecahydro-monocarba-closo-dodecaborate: KCB11H12

MCB11H12 (M: Li, Na) dodecahydro-monocarba-closo-dodecaborate salt compounds are known to have stellar superionic Li+ and Na+ conductivities in their high-temperature disordered phases, making them potentially appealing electrolytes in all-solid-state batteries. Nonetheless, it is of keen interest to search for other related materials with similar conductivities while at the same time exhibiting even lower (more device-relevant) disordering temperatures, a key challenge for this class of materials. With this in mind, the unknown structural and dynamical properties of the heavier KCB11H12 congener were investigated in detail by x-ray powder diffraction, differential scanning calorimetry, neutron vibrational spectroscopy, nuclear magnetic resonance, quasielastic neutron scattering, and AC impedance measurements. This salt indeed undergoes an entropy-driven, reversible, order-disorder transformation and with a lower onset temperature (348 K upon heating) in comparison to the lighter LiCB11H12 and NaCB11H12 analogues. The K+ cations in both the low- T ordered monoclinic ( P 2 1 / c ) and high- T disordered cubic (Fm-3m) structures occupy octahedral interstices formed by theCB 11 H 12 - anions. In the low- T structure, the anions orient themselves so as to avoid close proximity between their highly electropositive C-H vertices and the neighboring K+ cations. In the high- T structure, the anions are orientationally disordered, although to best avoid the K+ cations, the anions likely orient themselves so that their C-H axes are aligned in one of eight possible directions along the body diagonals of the cubic unit cell. Across the transition, anion reorientational jump rates change from 6.2×106 s-1 in the low- T phase (332 K) to 2.6×1010 s-1 in the high- T phase (341 K). In tandem, K+ conductivity increases by about thirty-fold across the transition, yielding a high- T phase value of 3.2×10-4 S cm-1 at 361 K. Yet, this is still about one to two orders of magnitude lower than that observed for LiCB11H12 and NaCB11H12, suggesting that the relatively larger K+ cation is much more sterically hindered than Li+ and Na+ from diffusing through the anion lattice via the network of smaller interstitial sites.

Hydrated Metal Ion Salts of the Weakly Coordinating Fluoroanions PF6-, TiF62-, B12F122-, Ga(C2F5)4-, B(3,5-C6H3(CF3)2)4-, and Al(OC(CF3)3)4-. In Search of the Weakest HOH···F Hydrogen Bonds

FTIR spectra of microcrystalline samples of 11 metal ion salt hydrates of a variety of weakly coordinating fluoroanions are reported. The compounds studied were Li(H₂O)₄(Al(OC(CF₃)₃)₄), Li(H₂O)(B(3,5-C₆H₃(CF₃)₂)₄), Li(H₂O)_n(Ga(C₂F₅)₄), Li(H₂O)(PF₆), Li₂(H₂O)₂(TiF₆), Li₂(H₂O)₄(B₁₂F₁₂), Na(H₂O)(PF₆), Na₂(H₂O)₂(B₁₂F₁₂), K₂(H₂O)₂(B₁₂F₁₂), Rb₂(H₂O)₂(B₁₂F₁₂), Cs₂(H₂O)(B₁₂F₁₂), and their partially or completely deuterated isotopologs and isotopomers. The O-D···F hydrogen bonds in Li(HOD)(H₂O)₃(Al(OC(CF₃)₃)₄) (ν(OD) = 2706 cm^-1), Li(HOD)(B(3,5-C₆H₃(CF₃)₂)₄) (ν(OD) = 2705 cm^-1), and Li(HOD)(H₂O)_n(Ga(C₂F₅)₄) (ν(OD) = 2697 cm^-1) rival HOD absorbed in polyvinylidene difluoride (ν(OD) = 2696 cm^-1) and HOD···FCH₃ in a frozen Ar matrix (ν(OD) = 2685 cm^-1) for the weakest hydrogen bonds between a water molecule and an F atom in any compound. As weak as they are, minor differences in O-H···F hydrogen bonds in the same fluoroanion salt can be distinguished spectroscopically. Uncoupled HOD molecules in asymmetric F···HOD···F' hydrogen bonding environments in Rb⁺, Cs⁺, Mg²⁺, and Co²⁺ hydrates of B₁₂F₁₂^2- gave rise to two observable ν(OD) bands even though the two R(O···F) distances differ by only 0.010(4) Å (Mg²⁺), 0.033(2) Å (Co²⁺), 0.074(4) Å (Rb⁺), and 0.106(6) Å (Cs⁺). A plot of ν(OD) for hydrates with a single uncoupled HOD molecule per metal ion (e.g., Li(HOD)(H₂O)₃(Al(OC(CF₃)₃)₄)) vs R(O···F) distance from single-crystal X-ray or neutron diffraction structures was prepared. The ν(OD) values range from 2305 to 2706 cm^-1 and the R(O···F) distances range from 2.58 to 3.17 Å. The plot consists of 53 {ν(OD), R(O···F)} data points, 23 of which are new and have ν(OD) > 2600 cm^-1, in contrast to a 1994 ν(OD) vs R(O···F) plot with 28 data points, none of which had ν(OD) > 2600 cm^-1. There is a clear and significant difference between the new ν(OD) vs R(O···F) plot and a literature ν(OD) vs R(O···O) plot for hydrates containing O-D···O hydrogen bonds. For a given ν(OD) stretching frequency, the exponential regression curves show that R(O···F) is typically 0.1-0.2 Å shorter than R(O···O), in harmony with the lower basicity and smaller size of F atoms vs O atoms.

Na+[Me3NB12Cl11]-·SO2: a rare example of a sodium-SO2 complex

In the title compound, the SO₂ mol­ecule is η¹-O-coordinated to the Na⁺ cation. The Na⁺ cation has a coordination number of eight in a distorted twofold capped trigonal prism and makes contacts to three individual boron cluster anions resulting in an overall three-dimensional network.

In the title compound, Na⁺[Me₃NB₁₂Cl₁₁]⁻·SO₂ [systematic name: sodium 1-(trimethylammonio)­undeca­chloro-closo-dodeca­borate sulfur dioxide], the SO₂ mol­ecule is η¹-O-coordinated to the Na⁺ cation. Surprisingly, the SO₂ mol­ecule is more weakly bound to sodium than is found in other sodium–SO₂ complexes and the SO₂ mol­ecule is essentially undistorted compared to the structure of free SO₂. The Na⁺ cation has a coordination number of eight in a distorted twofold-capped trigonal prism and makes contacts to three individual boron cluster anions, resulting in an overall three-dimensional network. Although the number of known η¹-O-coordinated SO₂ complexes is growing, sodium-SO₂ complexes are still rare.

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.

Properties of perhalogenated {closo-B10} and {closo-B11} multiply charged anions and a critical comparison with {closo-B12} in the gas and the condensed phase

Dependence of electronic properties and reactivity of closo-borates with size and halogen substituent was investigated.

Manifestations of Weak O-H···F Hydrogen Bonding in M(H2O) n(B12F12) Salt Hydrates: Unusually Sharp Fourier Transform Infrared ν(OH) Bands and Latent Porosity (M = Mg-Ba, Co, Ni, Zn)

Eight M(H₂O) _n(Z) salt hydrates were characterized by single-crystal X-ray diffraction (Z^2- = B₁₂F₁₂^2-): M = Ca, Sr, n = 7; M = Mg, Co, Ni, Zn, n = 6; M = Ba, n = 4, 5. Weak O-H···F hydrogen bonding between the M(H₂O) _n²⁺ cations and Z^2- resulted in room-temperature Fourier transform infrared (FTIR) spectra having sharp ν(OH) bands, with full widths at half max of 10-30 cm^-1, which are much more narrow than ν(OH) bands in room temperature FTIR spectra of most salt hydrates. Clearly resolved ν_asym(OH/OD) and ν_sym(OH/OD) bands with Δν(OH) as small as 17 cm^-1 and Δν(OD) as small as 11 cm^-1 were observed (Δν(OX) = ν_asym(OX) - ν_sym(OX)). The isomorphic hexahydrates ( R3̅) have two fac-(H₂O)₃ sets of H₂O ligands and nearly octahedral coordination spheres. They exhibited four resolvable ν(OH) bands, one ν_asym(OH)/ν_sym(OH) pair for H₂O ligands with longer O(H)···F distances and one ν_asym(OH)/ν_sym(OH) pair for H₂O ligands with shorter O(H)···F distances. The ν(OH) bands for the three H₂O molecules with shorter, slightly stronger O(H)···F hydrogen bonds were broader, more intense, and red-shifted by ca. 25 cm^-1 relative to the bands for the three other H₂O molecules, the first time that such small differences in relatively weak O(H)···F hydrogen bonds in the same crystalline hexahydrate have resulted in observable IR spectroscopic differences at room temperature. For the first time room temperature ν(OH) values for salt hexahydrates showed the monotonic progression Mg²⁺ > Co²⁺ > Ni²⁺ > Zn²⁺, essentially the same progression as the p K_a values for these metal ions in aqueous solution. A further manifestation of the weak O-H···F hydrogen bonding in these hydrates is the latent porosity exhibited by Ba(H₂O)_5,8(Z), Sr(H₂O) _n,m(Z), and Ca(H₂O)_4,6(Z). Finally, the H₂O/D₂O exchange reaction Co(D₂O)₆(Z) → Co(H₂O)₆(Z) was ca. 50% complete in 1 h at 50 °C in N₂/17 Torr H₂O( g).

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

This Review gives a comprehensive overview of the most topical weakly coordinating anions (WCAs) and contains information on WCA design, stability, and applications. As an update to the 2004 review, developments in common classes of WCA are included. Methods for the incorporation of WCAs into a given system are discussed and advice given on how to best choose a method for the introduction of a particular WCA. A series of starting materials for a large number of WCA precursors and references are tabulated as a useful resource when looking for procedures to prepare WCAs. Furthermore, a collection of scales that allow the performance of a WCA, or its underlying Lewis acid, to be judged is collated with some advice on how to use them. The examples chosen to illustrate WCA developments are taken from a broad selection of topics where WCAs play a role. In addition a section focusing on transition metal and catalysis applications as well as supporting electrolytes is also included.

The closo-Dodecaborate Dianion Fused with Oxazoles Provides 3D Diboraheterocycles with Selective Antimicrobial Activity

The synthesis and application of icosahedral boron cluster compounds has been studied extensively since their discovery several decades ago; however, two aspects of their chemistry have received little attention: The possibility to form inorganic/organic fused boraheterocycles and their potential to act as antimicrobial agents. This work comprises the preparation of a class of 3D diborabenzoxazole analogues with the closo-dodecaborate in place of the benzene moiety. The presented synthetic procedures provide access to a wide range of diboraheterocycles under mild conditions. These 3D heterocycles exhibit strong and selective antimicrobial activity against Neisseria gonorrhoeae, a widespread bacterial pathogen that has shown increasing incidences of multidrug resistance and for which the development of new antimicrobial compounds is urgently needed.

Synthesis and Applications of Perfunctionalized Boron Clusters

This Viewpoint describes major advances pertaining to perfunctionalized boron clusters in synthesis and their respective applications. The first portion of this work highlights key synthetic methods, allowing one to access a wide range of polyhedral boranes (B4 and B6-B12 cluster cores) that contain exhaustively functionalized vertices. The second portion of this Viewpoint showcases the historical developments in using these molecules for applications ranging from materials science to medicine. Last, we suggest potential new directions for these clusters as they apply to both synthetic methods and applications.

A series of pentanary inorganic supramolecular sulfides (A3X)[MB12(MS4)3] (A = K, Cs; X = Cl, Br, I; M = Ga, In, Gd) featuring B12S12 clusters

A series of multinary thiogallate- or thioindate-closo-dodecaborates synthesized by solid state reactions demonstrate second-harmonic generation behaviors.