Structural characterization of a trio of hydride-bridged sodium aluminate compounds

The synthesis and single-crystal structures of three hydride bridged sodium aluminate compounds containing the utility amide N(SiMe3)2 (HMDS) are reported. Both (HMDS)2Al(H)2Na(THF)(PMEDTA), (1) (THF = tetrahydrofuran, PMDETA = N,N,N′,N′′,N′′-pentamethyldiethylenetriamine) and [(HMDS)2Al(H)2Na(THF)2]2 (2) are dihydrides. However, 1 is a dinuclear Al—H—Na monomer with one bridging and one terminal hydride ligand whilst in 2 all the hydride ligands bridge between Al and Na to give a dimeric structure with a core (AlHNaH)2 eight-membered ring. In contrast the structure of [(HMDS)Al(H)3Na(PMEDTA)]2 (3) also contains a (AlHNaH)2 eight-membered ring but is a trihydride with two bridging and one terminal hydride per Al centre. The (AlHNaH)2 eight-membered rings of 2 and 3 differ in their structural details. That of 2 is based around a 2-fold axis and has a larger Al···Al intra-ring distance than that found in centrosymmetric 3.