The development of high energy density and high efficiency hydrogen storage materials is widely considered to be one of the most challenging barriers to the adoption of fuel cell power trains in transportation applications. Magnesium forms a high hydrogen gravimetric density (14.9wt%) tetrahydroborate (Mg(BH4)2) with a relatively low decomposition temperature (Tdec ~ 300C). We have identified and obtained a structural solution for a new low temperature cubic polymorph of Mg(BH4)2. Furthermore, we have identified a novel transformation process with 2 further, novel, polymorphs. We request 2 days on WISH to perform a detailed study of Mg(11BD4)2 in order to probe the structural evolution and build a clear picture of the decomposition of the tetrahydroborate. These studies will allow us to determine mechanisms and hence to develop materials with improved functional properties.