The mechanochemical reaction of LiBH4 with MnCl2 produces the neutral complex Mn(BH4)2. Thermal desorption studies show that the mechanochemical reaction of NaBH4 with MnCl2produces a different species, apparently Na2Mn(BH4)4, that undergoes dehydrogenation of a much lower weight percent H at a ~20 °C higher temperature than the neutral Mn(BH4)2. Vibrational spectroscopy also reveals that a complex manganese borohydride(s) in addition to Mn(BH4)2 are formed from the mechanochemical reactions. Analysis of the vibrational spectra in conjunction with DFT calculations on a model Mn(BH4)42− complex suggest bidentate binding of the [BH4]− ligands to the Mn center in the anionic complex. The calculated highest frequencies of the B−H stretching modes (corresponding to the "free" B−H bonds) agree well with the experimental frequencies and support the presence of this structural feature.