The hydrogen in the complex hydrides is located in the
corners of a tetraeder with boron or aluminum in the center.
The negative charge of the anion, [BH4] and [AlH4] is
compensated by a cation, e.g. Li or Na. The hydride complexes
of borane, the tetrahydroborates M(BH4), and of
alane the tetrahydroaluminate M(AlH4) are interesting storage
materials, however, they were known to be stable and
decompose only at elevated temperatures and often above
the melting point of the complex.