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Synthesis and Characterization of Methylammonium Borohydride

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journal contribution
posted on 07.02.2011, 00:00 authored by Kathryn R. Graham, Mark E. Bowden, Tim Kemmitt
A new borohydride, [CH3NH3]+[BH4], has been synthesized through the metathesis of CH3NH3F and NaBH4 in methylamine. Room-temperature X-ray diffraction studies have shown that [CH3NH3]+[BH4] adopts a tetragonal unit cell with considerable hydrogen mobility similar to that observed in NH3BH3. The kinetics and thermodynamics of hydrogen release have been investigated and were found to follow a similar pathway to that of [NH4]+[BH4]. Decomposition of [CH3NH3]+[BH4] occurred slowly at room temperature and rapidly at ca. 40 °C to form [BH2(CH3NH2)2]+[BH4], the methylated analogue of the diammoniate of diborane. The decomposition has been investigated by means of in situ X-ray diffraction and solid state 11B NMR spectroscopy and occurred 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 synthesized through analogous routes, indicating a more general applicability of the synthetic method.