In general, complex metal hydrides have the formula MMH, where M is an alkali metal cation or cation complex and M is a metal or metalloid.  Well known examples feature group 13 elements, especially boron and aluminium including sodium aluminium hydride, NaAlH ), lithium aluminium hydride, LiAlH, and lithium borohydride, (LiBH).  Complex metal hydrides are often soluble in etherial solvents.  Other complex metal hydrides are numerous.  Illustrative examples include the salts [MgBr(THF)]FeH and KReH.