Synthesis and Characterization of Methylammonium Borohydride
A new borohydride, [CH3NH3]+[BH4]-, has been synthesised by the metathesis of CH3NH3X and MBH4 in methylamine in order to determine its behaviour in comparison to ammonium borohydride [NH4]+[BH4]-. The introduction of methyl groups is expected to disrupt the hydrogen bonding network of [NH4]+[BH4]- and in turn alter the hydrogen release properties. Room temperature X-ray diffraction studies have shown that [CH3NH3]+[BH4]- adopts a tetragonal unit cell with lattice parameters of a = 4.9486 Å and b = 8.9083 Å. The room temperature structure shows considerable hydrogen mobility similar to that observed in NH3BH3. The kinetics and thermodynamics of these reactions have been investigated and show hydrogen release follows a similar pathway to that of [NH4]+[BH4]-. Both compounds decompose slowly at room temperature and rapidly at ca. 40 °C to form the diammoniate of diborane or the methylated analogue [BH2(CH3NH2)2]+BH4-. The first stage of decomposition has been further investigated by means on in-situ X-ray diffraction and solid state 11B NMR spectroscopy, and appears to occur in the absence of any detectable intermediates to form crystalline [BH2(CH3NH2)2]+BH4-. [(CH3)2NH2]+[BH4]- and [BH2{(CH3)2NH}2]+BH4- have also been synthesised by analogous routes, indicating a more general applicability of the synthetic method.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1007353
- Report Number(s):
- PNNL-SA-74583; INOCAJ; 25661; KP1704020; TRN: US201106%%232
- Journal Information:
- Inorganic Chemistry, 50(3):932-936, Vol. 50, Issue 3; ISSN 0020-1669
- Country of Publication:
- United States
- Language:
- English
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