Synthesis and characterization of methylammonium borohydride

A new borohydride, CH(3)NH(3)](+)BH(4)](-), has been synthesized through the metathesis of CH(3)NH(3)F and NaBH(4) in methylamine. Room-temperature X-ray diffraction studies have shown that CH(3)NH(3)](+)BH(4)](-) adopts a tetragonal unit cell with considerable hydrogen mobility similar to that observed in NH(3)BH(3). The kinetics and thermodynamics of hydrogen release have been investigated and were found to follow a similar pathway to that of NH(4)](+)BH(4)](-). Decomposition of CH(3)NH(3)](+)BH(4)](-) occurred slowly at room temperature and rapidly at ca. 40 °C to form BH(2)(CH(3)NH(2))(2)](+)BH(4)](-), the methylated analogue of the diammoniate of diborane. The decomposition has been investigated by means of in situ X-ray diffraction and solid state (11)B NMR spectroscopy and occurred in the absence of any detectable intermediates to form crystalline BH(2)(CH(3)NH(2))(2)](+)BH(4)](-). (CH(3))(2)NH(2)](+)BH(4)](-) and BH(2){(CH(3))(2)NH}(2)](+)BH(4)](-) have also been synthesized through analogous routes, indicating a more general applicability of the synthetic method.