In this work, a series of Mn-based borohydrides were synthesized by mechanochemical milling of ABH4-MnCl2 (where A=Li, Na, K) under argon. Samples prepared by milling xLiBH4-MnCl2 (where x = 2 or 3) resulted in the formation of Mn(BH4)2 and LiCl in a stoichiometric ratio. Thermal decomposition of Mn(BH4)2 was observed between 105 and 180°C with the concurrent evolution of hydrogen and diborane. Analysis of the decomposition products suggested the presence of amorphous B, Mn and LiCl.
When NaBH4 was used as a reagent, Mn(BH4)2 was also observed, however instead of NaCl, a solid solution of NaClx(BH4)1−x and Na6MnCl8 were formed. Mn(BH4)2 decomposed between 110 and 170°C for xNaBH4-MnCl2 with the concurrent evolution of hydrogen and diborane. Analysis of the decomposed samples showed that amorphous B and Mn formed (110 to 170°C) and NaClx(BH4)1−x reacted with Na6MnCl8 to produce NaCl (250 to 475°C).
When KBH4 was used as a reagent, Mn(BH4)2 was not observed. Rather, K2Mn(BH4)4, KMnCl3 and unreacted KBH4 were observed. The mass losses for the milled sample were observed between 100 to 160°C with a release of hydrogen and trace diborane, forming KBH4, B, and Mn, and between 165 to 260°C with only hydrogen release, giving KCl, B and Mn