Enhanced Room-Temperature Ionic Conductivity of NaCB11H12 via High-Energy Mechanical Milling.

The body-centered cubic (bcc) polymorph of NaCB11H12 has been stabilized at room temperature by high-energy mechanical milling. Temperature-dependent electrochemical impedance spectroscopy shows an optimum at 45-min milling time, leading to an rt conductivity of 4 mS cm-1. Mechanical milling suppresses an order-disorder phase transition in the investigated temperature range. Nevertheless, two main regimes can be identified, with two clearly distinct activation energies. Powder X-ray diffraction and 23Na solid-state NMR reveal two different Na+ environments, which are partially occupied, in the bcc polymorph. The increased number of available sodium sites w.r.t. ccp polymorph raises the configurational entropy of the bcc phase, contributing to a higher ionic conductivity. Mechanical treatment does not alter the oxidative stability of NaCB11H12. Electrochemical test on a symmetric cell (Na|NaCB11H12|Na) without control of the stack pressure provides a critical current density of 0.12 mA cm-2, able to fully charge/discharge a 120 mA h g-1 specific capacity positive electrode at the rate of C/2.

Gaseous cyclodextrin-closo-dodecaborate complexes χCD·B12X122- (χ = α, ß, and γ; X = F, Cl, Br, and I): electronic structures and intramolecular interactions.

A fundamental understanding of cyclodextrin-closo-dodecaborate inclusion complexes is of great interest in supramolecular chemistry. Herein, we report a systematic investigation on the electronic structures and intramolecular interactions of perhalogenated closo-dodecaborate dianions B12X122- (X = F, Cl, Br and I) binding to α-, ß-, and γ-cyclodextrins (CDs) in the gas phase using combined negative ion photoelectron spectroscopy (NIPES) and density functional theory (DFT) calculations. The vertical detachment energy (VDE) of each complex and electronic stabilization of each dianion due to the CD binding (ΔVDE, relative to the corresponding isolated B12X122-) are determined from the experiments along α-, ß- and γ-CD in the form of VDE (ΔVDE): 4.00 (2.10), 4.33 (2.43), and 4.30 (2.40) eV in X = F; 4.09 (1.14), 4.64 (1.69), and 4.69 (1.74) eV in X = Cl; 4.11 (0.91), 4.58 (1.38), and 4.70 (1.50) eV in X = Br; and 3.54 (0.74), 3.88 (1.08), and 4.05 (1.25) eV in X = I, respectively. All complexes have significantly higher VDEs than the corresponding isolated dodecaborate dianions with ΔVDE spanning from 0.74 eV at (α, I) to 2.43 eV at (ß, F), sensitive to both host CD size and guest substituent X. DFT-optimized complex structures indicate that all B12X122- prefer binding to the wide openings of CDs with the insertion depth and binding motif strongly dependent on the CD size and halogen X. Dodecaborate anions with heavy halogens, i.e., X = Cl, Br, and I, are found outside of α-CD, while B12F122- is completely wrapped by γ-CD. Partial embedment of B12X122- into CDs is observed for the other complexes via multipronged B-XH-O/C interlocking patterns. The simulated spectra based on the density of states agree well with those of the experiments and the calculated VDEs well reproduce the experimental trends. Molecular orbital analyses suggest that the spectral features at low binding energies originated from electrons detached from the dodecaborate dianion, while those at higher binding energies are derived from electron detachment from CDs. Energy decomposition analyses reveal that the electrostatic interaction plays a dominating role in contributing to the host-guest interactions for the X = F series partially due to the formation of a O/C-HX-B hydrogen bonding network, and the dispersion forces gradually become important with the increase of halogen size.

Activation of CS2 and CO2 by Silylium Cations.

The hydride-bridged silylium cation [Et3 Si-H-SiEt3 ]+ , stabilized by the weakly coordinating [Me3 NB12 Cl11 ]- anion, undergoes, in the presence of excess silane, a series of unexpected consecutive reactions with the valence-isoelectronic molecules CS2 and CO2 . The final products of the reaction with CS2 are methane and the previously unknown [(Et3 Si)3 S]+ cation. To gain insight into the entire reaction cascade, numerous experiments with varying conditions were performed, intermediate products were intercepted, and their structures were determined by X-ray crystallography. Besides the [(Et3 Si)3 S]+ cation as the final product, crystal structures of [(Et3 Si)2 SMe]+ , [Et3 SiS(H)Me]+ , and [Et3 SiOC(H)OSiEt3 ]+ were obtained. Experimental results combined with supporting quantum-chemical calculations in the gas phase and solution allow a detailed understanding of the reaction cascade.

Synthesis, Electronic Properties and Reactivity of [B12 X11 (NO2 )]2- (X=F-I) Dianions.

Nitro-functionalized undecahalogenated closo-dodecaborates [B12 X11 (NO2 )]2- were synthesized in high purities and characterized by NMR, IR, and Raman spectroscopy, single crystal X-diffraction, mass spectrometry, and gas-phase ion vibrational spectroscopy. The NO2 substituent leads to an enhanced electronic and electrochemical stability compared to the parent perhalogenated [B12 X12 ]2- (X=F-I) dianions evidenced by photoelectron spectroscopy, cyclic voltammetry, and quantum-chemical calculations. The stabilizing effect decreases from X=F to X=I. Thermogravimetric measurements of the salts indicate the loss of the nitric oxide radical (NO. ). The homolytic NO. elimination from the dianion under very soft collisional excitation in gas-phase ion experiments results in the formation of the radical [B12 X11 O]2-. . Theoretical investigations suggest that the loss of NO. proceeds via the rearrangement product [B12 X11 (ONO)]2- . The O-bonded nitrosooxy structure is thermodynamically more stable than the N-bonded nitro structure and its formation by radical recombination of [B12 X11 O]2-. and NO. is demonstrated.

First steps towards a stable neon compound: observation and bonding analysis of [B12(CN)11Ne].

Noble gas (Ng) containing molecular anions are much scarcer than Ng containing cations. No neon containing anion has been reported so far. Here, the experimental observation of the molecular anion [B12(CN)11Ne]- and a theoretical analysis of the boron-neon bond is reported.

[Se(CH2C(O)CH3)3][B12F11NH3]: The first selenium cation with three ß-ketone substituents.

The reaction of [Se8][B12F11NH3]2 with acetone and subsequent crystallization from acetone/diethyl ether yielded the selenium cation [Se(CH2C(O)CH3)3]+ as a by-product, which is stabilized by the weakly coordinating undeca-fluorinated anion [B12F11NH3]-. While attempting to crystallize pure [Se8][B12F11NH3]2, the structure of the isolated product, namely, tris-(2-oxoprop-yl)selenium 1-ammonio-undeca-fluoro-dodeca-borate, was surprising. The cation [Se(CH2C(O)CH3)3]+ represents the first example for a cationic selenium compound with three ketone functional groups located in the ß-position with respect to the selenium atom. The cation possesses almost trigonal-pyramidal C 3 symmetry and forms hydrogen bonds to the ammonio group of the anion.