Crystal structure of [Al4(OH)6(H2O)12][Al(H2O)6]2Br12: a new polyaluminum compound.

A vertex-shared tetrahedral [Al4(OH)6(H2O)12]6+ (Al4) and a disordered [Al(H2O)6]3+ (Al1) that coexist in a 1:2 ratio within each unit cell were observed in the structure of [Al4(OH)6(H2O)12][Al(H2O)6]2Br12, which crystallized in a cubic Fd3m space group from a spontaneously hydrolyzed solution of AlBr3. The former is composed of four AlO6 octahedra that are connected to each other by sharing three vertexes of each octahedron and form a large regular tetrahedron with ideal Td symmetry. The central Al3+ ion of the latter is coordinated by 6 disordered OH2 molecules, that form a core–shell structure with ideal D3d symmetry.