Redetermination of di-μ-hydrido-hexa­hydridotetra­kis(tetra­hydro­furan)dialuminium(III)magnesium(II)

The structure of the title compound, [Mg(AlH4)2(C4H8O)4], has been redetermined at 150 K. The MgII ion is hexa­coordinated to four tetra­hydro­furan (THF) ligands, and two AlH4 − anions through bridging H atoms. The Al—H distances are more precise compared to those previously determined [Nöth et al. (1995 ▶). Chem. Ber. 128, 999–1006; Fichtner & Fuhr (2002 ▶). J. Alloys Compd, 345, 386–396]. The mol­ecule has twofold rotation symmetry

Desolvation and Dehydrogenation of Solvated Magnesium Salts of Dodecahydrododecaborate: Relationship between Structure and Thermal Decomposition

Attempts to synthesize solvent-free MgB_(12)H_(12) by heating various solvated forms (H_2O, NH_3, and CH_3OH) of the salt failed because of the competition between desolvation and dehydrogenation. This competition has been studied by thermogravimetric analysis (TGA) and temperature-programmed desorption (TPD). Products were characterized by IR, solution- and solid-state NMR spectroscopy, elemental analysis, and single-crystal or powder X-ray diffraction analysis. For hydrated salts, thermal decomposition proceeded in three stages, loss of water to form first hexahydrated then trihydrated, and finally loss of water and hydrogen to form polyhydroxylated complexes. For partially ammoniated salts, two stages of thermal decomposition were observed as ammonia and hydrogen were released with weight loss first of 14 % and then 5.5 %. Thermal decomposition of methanolated salts proceeded through a single step with a total weight loss of 32 % with the release of methanol, methane, and hydrogen. All the gaseous products of thermal decomposition were characterized by using mass spectrometry. Residual solid materials were characterized by solid-state 11B magic-angle spinning (MAS) NMR spectroscopy and X-ray powder diffraction analysis by which the molecular structures of hexahydrated and trihydrated complexes were solved. Both hydrogen and dihydrogen bonds were observed in structures of [Mg(H_2O_6B_(12)H_(12)]⋅6 H_2O and [Mg(CH_3OH)_(6)B_(12)H_(12)]⋅6 CH_3OH, which were determined by single-crystal X-ray diffraction analysis. The structural factors influencing thermal decomposition behavior are identified and discussed. The dependence of dehydrogenation on the formation of dihydrogen bonds may be an important consideration in the design of solid-state hydrogen storage materials

Anti and gauche conformers of an inorganic butane analogue, NH3BH2NH2BH3

The crystal structures of an inorganic butane analogue, NH3BH2NH2BH3 (DDAB), were determined using single crystal X-ray diffraction, revealing both anti and gauche conformations. The anti conformation is stabilized by intermolecular dihydrogen bonds in the crystal whereas two gauche conformations of DDAB observed in its 18-crown-6 adducts are stabilized by an intramolecular dihydrogen bond. The two gauche conformations show rotational isomerization but whether they are a pair of enantiomers is yet to be defined

Li2B12H12·7NH3: a new ammine complex for ammonia storage or indirect hydrogen storage

A new ammine complex, Li2B12H12$7NH3, that can reversibly release all the NH3 at below 200oC and reabsorb NH3 at room temperature and 0.5 bar was synthesized and investigated for reversible ammonia storage or indirect hydrogen storage

Inter­molecular di­hydrogen- and hydrogen-bonding inter­actions in di­ammonium closo-deca­hydro­deca­borate sesquihydrate

The asymmetric unit of the title salt, 2NH4+_B10H102__1.5H2O or (NH4)2B10H10_1.5H2O, (I), contains two B10H102_ anions, four NH4+ cations and three water molecules. (I) was converted to the anhydrous compound (NH4)2B10H10, (II), by heating to 343 K and its X-ray powder pattern was obtained. The extended structure of (I) shows two types of hydrogen-bonding interactions (N-H_ _ _O and O-H_ _ _O) and two types of dihydrogen-bonding interactions (N- H_ _ _H-B and O-H_ _ _H-B). The N-H_ _ _H-B dihydrogen bonding forms a two-dimensional sheet structure, and hydrogen bonding (N-H_ _ _O and O-H_ _ _O) and O- H_ _ _H-B dihydrogen bonding link the respective sheets to form a three-dimensional polymeric network structure. Compound (II) has been shown to form a polymer with the accompanying loss of H2 at a faster rate than (NH4)2B12H12 and we believe that this is due to the stronger dihydrogenbonding interactions shown in the hydrate (I)

Synthesis, structural characterization, and thermal decomposition study of Mg(H2O)6B10H10·4H2O

Compound 1 (Mg(H2O)6B10H10 3 4H2O) was synthesized and characterized using NMR, IR, XRD, and elemental analysis. Its thermal decomposition behavior was studied using Simultaneous Thermogravimetric Modulated Beam Mass Spectrometry (STMBMS), TGA, DSC, IR, and 11B NMR. The crystal structure of 1 reveals multiple dihydrogen and hydrogen bonding interactions that form a 3D extended structure. A reaction network characterizing the thermal decomposition of 1 and its secondary products over a temperature range from 20 to 1000 _C has been developed. Thermal decomposition of 1 is primarily controlled by two competing branches in the reaction network, where coordinated water evolves as either H2O (dehydration) or H2 (dehydrogenation). The extent of reaction to form H2 depends on the fraction of the coordinated water remaining in the sample when its temperature is between 160 and 225 _C. The evolution of coordinated water is reversible and controlled by dissociative sublimation. For the release of coordinated water between 160 and 215 _C, the vapor pressure of water is given by Loge P (Torr) = 30.4561 _ 12425.2/T (K) and ΔHs = 103.3(0.3 kJ/mol. The nature of the condensed phase secondary product remaining after all coordinated water is removed by either dehydration and/or dehydrogenation depends strongly on the extent of reaction to form Mg(OH)xB10H10_x. Results of STMBMS experiments where x varies from 0.2 to ∼4 are used to develop the reaction network that characterizes the thermal decomposition process. Heating of 1 at 205 _C resulted in the formation of water-soluble Mg(OH)x(H2O)2_xB10H10_x, while prolonged heating of 1 at 270 _C and heating up to 1000 _C led to decompositio

Thermal Decomposition Behavior of Hydrated Magnesium Dodecahydrododecaborates

MgB₁₂H₁₂ is an intermediate in the hydrogen desorption and sorption processes of magnesium borohydride, which is an important candidate material for hydrogen storage. It is thus highly desirable to synthesize anhydrous MgB₁₂H₁₂ in order to study its properties and its role in the hydrogenation and dehydrogenation of magnesium borohydride. Contrary to the literature claim, we find that anhydrous MgB₁₂H₁₂ cannot be obtained from simple thermal decomposition of Mg(H₂O)₆B₁₂H₁₂·6H₂O (<b>1</b>) which has different thermal decomposition behavior from that of most hydrated alkali and alkaline earth salts of dodecahydrododecaborates. Thermal decomposition of <b>1</b> involves both dehydration and dehydrogenation processes in three steps, resulting in the formation of complexes Mg(H₂O)₆B₁₂H₁₂ (<b>2</b>), Mg(H₂O)₃B₁₂H₁₂ (<b>3</b>), and Mg(μ-OH)_<i>x</i>B₁₂H_{12−<i>x</i>} (<b>4</b>) that were characterized by XRD, IR, and ¹¹B NMR. Dehydrogenation was also confirmed by both the generation of hydrogen observed in TPD-MS spectra and the formation of polyhydroxylated complexes