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Hydrogen release from ammonia borane (NH(3)BH(3), AB) can be greatly promoted by mechanical milling with magnesium nitride (Mg(3)N(2)). For example, a post-milled 6AB/Mg(3)N(2) sample started to release hydrogen from similar to 65 degrees C and gave a material-based hydrogen capacity of similar to 11 wt% upon heating to 300 degrees C. In addition to the improved dehydrogenation kinetics, the 6AB/Mg(3)N(2) sample also showed satisfactory performance in suppressing the volatile byproducts. X-ray diffraction, Fourier transform infrared spectroscopy and solid-state (11)B MAS NMR, as well as a series of designed experiments, were carried out to gain mechanistic understanding of the property improvements that arise from addition of Mg(3)N(2). Our study found that the formation of 3Mg(NH(2)BH(3))(2)center dot 2NH(3), which is in single or mixed amidoborane ammoniate phases in nature, is an important mechanistic step in the dehydrogenation process of the 6AB/Mg(3)N(2) sample.