The continuing story of the diammoniate of diborane

The diammoniate of diborane ([H2B(NH3)2][BH4], DADB) is an ionic dimer of ammonia borane (H3NBH3, AB). It has received much less attention in the past few decades than AB, although it has the same high hydrogen content (19.6%). In this review, the important events in the development of DADB are summarized: its serendipitous discovery, formulation, characterization, formation mechanism, preparation, and relationship with AB. Focus is given to its competing formation with AB and potential application as a hydrogen storage medium.