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 Fd3̅m 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.在[Al4(OH)6(H2O)12][Al(H2O)6]2Br12的晶体结构中，观测到每个晶胞内以1:2的比例共存两种铝配合物：一种为顶点共享型四面体结构的[Al4(OH)6(H2O)12]6+（简称Al4），另一种为无序结构的[Al(H2O)6]3+（简称Al1）。该晶体由AlBr3的自发水解溶液结晶得到，所属空间群为立方Fd-3m。前者由四个AlO6八面体构成，每个八面体通过共享三个顶点与其余八面体相互连接，形成具有理想Td对称性的大尺寸正四面体结构。后者的中心Al³+离子与六个无序配位水分子配位，构建出具有理想D3d对称性的核壳结构。