Structural characterization of three hydride-bridged sodium aluminate compounds

The synthesis and single-crystal structures of three hydride-bridged sodium aluminate compounds containing the utility amide HMDS [N(SiMe3)2 or C6H18NSi2] are reported. Both bis­[bis­(tri­methyl­sil­yl)amido-2κN]-μ-hydrido-hydrido-2κH-(N,N,N′,N′′,N′′-penta­methyl­diethylenetri­amine-1κ3 N,N′,N′′)(tetrahydro­furan-1κO)aluminiumsodium, [AlNa(C6H18NSi2)2H2(C4H8O)(C9H23N3)] or (HMDS)2Al(H)2Na(THF)(PMDETA), (1) (THF = tetra­hydro­furan, C4H8O; PMDETA = N,N,N′,N′′,N′′-penta­methyl­diethylenetri­amine, C9H23N3) and tetra­kis­[bis­(tri­methyl­sil­yl)amido]-3κ2 N,4κ2 N-Tetra-μ-hydrido-Tetra­kis­(tetra­hydro­furan)-1κ2 O,2κ2 O-dialuminiumdisodium, [Al2Na2(C6H18NSi2)4H4(C4H8O)4] or [(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 atoms to give a dimeric structure with a core (AlHNaH)2 eight-membered ring. In contrast, the structure of bis­[bis­(tri­methyl­sil­yl)amido]-3κN,4κN-dihydrido-3κH,4κH-Tetra-μ-hydrido-bis(N,N,N′,N′′,N′′-penta­methyl­diethylenetri­amine)-1κ3 N,N′,N′′;2κ3 N,N′,N′′-dialuminiumdisodium, [Al2Na2(C6H18NSi2)2H6(C9H23N3)2] or [(HMDS)Al(H)3Na(PMDETA)]2 (3), also contains a (AlHNaH)2 eight-membered ring but is a trihydride with two bridging and one terminal hydride ligand 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 twofold axis and has a larger Al⋯Al intra-ring distance than that found in centrosymmetric 3.