Synthesis and structure of triphenylmethylphosphonium tetrakis(tetrahydroborato)aluminate, (Ph3MeP)(Al(BH4)4), an example of eight-coordinate aluminum(III)

Reaction of Al(BH4)3 with (BH4)- produces stable, crystalline solids of ((Ph3P)2N)+ and (Ph3MeP)+ salts of the tetrakis(tetrahydroborato)aluminate anion (Al(BH4)4)-. Multinuclear NMR spectroscopic studies help characterize these salts, and single-crystal X-ray studies facilitate the determination of the structure of (Ph3MeP)(Al(BH4)4). The aluminum compound has an eight-coordinated Al atom and the Al center is surrounded by distorted dodecahedral coordination geometry formed by the eight bridging hydrogens.