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Mg(B3H8)2 is a crucial reaction intermediate in the thermal decomposition of the hydrogen storage material Mg(BH4)2 and is discussed as a potential solid-state Mg-ion conductor. We successfully synthesized unsolvated Mg(B3H8)2 and highlight that Mg(B3H8)2 exists mainly as a low-dimensional solid. In addition, the Mg2+ conductivity was evaluated to be 1.4.10−4 S cm−1 at 80 °C. [ABSTRACT FROM AUTHOR]

Metal hydroborates from M(BH4)n to Mx(B12H12)y currently attract a strong interest for potential applications in the field of hydrogen storage and more recently as solid ionic conductors. While thermodynamic data for the alkali borohydrides (MBH4) are well known, experimental data for other compounds are cruelly lacking. Using a combination of theoretical (DFT) and experimental data, we calculate the lattice enthalpy for a series of borohydrides. The comparison with literature data show that these lattice enthalpies are very similar to those of the corresponding metal bromides. This similarity is at the origin of a good correlation between the formation enthalpy of bromides and borohydrides which is then used to estimate the previously unknown formation enthalpy of MII(BH4)2 (MII=divalent cation) and Ln(BH4)3 (Ln=lanthanide). The Gibbs free energy of formation of M2(B12H12) (M=alkali metal) is also estimated. [ABSTRACT FROM AUTHOR]

The characterization of boron-hydrogen compounds is an active research area which encompasses subjects as diverse as the chemistry and structures of closoboranes or the thermal decomposition mechanism of the borohydrides. Due to their high gravimetric hydrogen content, borohydrides are considered as potential hydrogen storage materials. Their thermal decompositions are multistep processes, for which the intermediate products are not easily identified. To help address this issue, we have extensively investigated the vibrational and NMR properties of 21 relevant B m H n z − boron-hydrogen species ( m = 1–12; n = 1–14; z = 0–2) within density functional theory. We could thus show that the B3LYP-D2 dispersion-corrected hybrid can be used in combination with the large cc-pVTZ basis set for the reliable prediction of the 11 B and 1 H NMR spectra of the boron-hydrogen species, and also for the reliable prediction of their IR and Raman spectra while taking into account the anharmonicity of their molecular vibrations. [ABSTRACT FROM AUTHOR]

B 12 H 12 2 − can be formed during the thermal decomposition of metal borohydrides ( M ( B H 4 ) x ) . Halogen ions such as fluoride or chloride can contribute to destabilize the B H 4 − ions. Hydride and fluoride mixed species like B 12 H n F ( 12 − n ) 2 − will be probable products after hydrogen release from mixed boro-hydride-fluoride ( B H x F ( 4 − x ) − ) or borohydride-borofluoride systems ( B H 4 − , B F 4 − ). Various number of isomers are possible for B 12 H n F ( 12 − n ) 2 − (n = 2–11). DFT calculations were performed on isolated ions of all the possible isomers for (n = 0–3, 9–12), using B3LYP functionals and 6-31G(d,p) basis set. Relative stability, vibrational and NMR spectroscopy of these isomers are discussed and compared with available experimental data. [ABSTRACT FROM AUTHOR]

Highlights: [•] A collection of FTIR spectra of borohydrides and deuterides is presented. [•] All spectra are available digitally for the research community. [•] This database is a new tool in the field of potential hydrogen storage materials. [•] This database will be continuously extended. [Copyright &y& Elsevier]

Abstract: A solid solution of magnesium and manganese borohydrides was studied by in situ synchrotron radiation X-ray powder diffraction and infrared spectroscopy. A combination of thermogravimetry, mass and infrared spectroscopy, and atomic emission spectroscopy were applied to clarify the thermal gas desorption of pure Mn(BH4)2 and a solid solution of composition Mg0.5Mn0.5(BH4)2. Mg x Mn(1− x )(BH4)2 (x= 0–0.8) conserves the trigonal structure of Mn(BH4)2 at room temperature. Manganese is dissolved in the hexagonal structure of α-Mg(BH4)2, with the upper solubility limit not exceeding 10mol.% at room temperature. There exists a two-phase region of trigonal and hexagonal borohydrides within the compositional range x =0.8–0.9 at room temperature. Infrared spectra show splitting of various vibrational modes, indicating the presence of two cations in the trigonal Mg x Mn(1− x )(BH4)2 solid solutions, as well as the appearance of a second phase, hexagonal α-Mg(BH4)2, at higher magnesium contents. All vibrational frequencies are shifted to higher values with increasing magnesium content. The decomposition temperature of the trigonal Mg x Mn(1− x )(BH4)2 (x= 0–0.8) does not vary significantly as a function of the magnesium content (433–453K). The desorbed gas contains mostly hydrogen and 3–7.5mol.% diborane B2H6, as determined from analyses of the Mn(BH4)2 and Mg0.5Mn0.5(BH4)2 samples. An eutectic relation between α-Mg(BH4)2 and LiBH4 is observed. The solid solution Mg x Mn(1− x )(BH4)2 is a promising material for hydrogen storage as it decomposes at a similar temperature to Mn(BH4)2, i.e. at a much lower temperature than pure Mg(BH4)2 without significantly losing hydrogen weight capacity thanks to substitution of Mn by Mg up to 80mol.%. The questions of diborane release and reversibility remain to be addressed. [Copyright &y& Elsevier]

Rare-earth borohydrides have recently attracted a strong interest as potential hydrogen storage materials. While the local structure of the BH 4 − ion can be probed using vibrational spectroscopy, the local structure of the rare-earth ion can be studied using luminescence spectroscopy. This is reported here for Tb(BH 4) 3 and its solvate with S(CH 3) 2. The spectra clearly show smaller CF splittings for the unsolvated compound. These experimental data are compared with recent DFT+U calculations of the energy levels and CF splittings for Tb(BH 4) 3 and show that these calculations significantly overestimate the experimental results. • The luminescence of Tb(BH 4) 3 and Tb(BH 4) 3 ·S(CH 3) 2 is reported for the first time. • Emission and excitation data reveal a difference in the local symmetry of Tb3+. • Tb3+ ions are differently affected by the crystal field within the two structures. • Calculated transition energies are compared to the emission spectrum of Tb(BH 4) 3. • The free ion and CF parameters predicted by a DFT+U methodology are overestimated. [ABSTRACT FROM AUTHOR]