Aluminum subhalides of the type Al(22)X(20).12L (X = Cl, Br; L = THF, THP) are the only known representatives of polyhedral aluminum subhalides and exhibit interesting multicenter bonding properties. Herein, we report on the synthesis and structural investigation of the first chlorides of this type. Additional investigations applying solid-state (27)Al NMR (MAS), XPS (of Al(4)Cp(4) and Al(22)X(20).12L), and quantum chemical calculations shed more light upon the structure of the molecules and possible Al modifications.
A disproportionation process of a metastable AlCl solution with a simultaneous ligand exchange-Cl is substituted by N(SiMe(3))(2)-leads to a [Al(69)[N(SiMe(3))(2)](18)](3-) cluster compound that can be regarded as an intermediate on the way to bulk metal formation. The cluster was characterized by an X-ray crystal structural analysis. Regarding its structure and the packing within the crystal, this metalloid cluster with 4 times more Al atoms than ligands is compared to the [Al(77)N(SiMe(3))(2)](20)](2-) cluster that has been published four years ago. Although there is a similar packing density of the Al atoms in both clusters as well as in Al metal, the X-ray structural analysis shows significant differences in topology and distance proportions. The differences between these-at a first glance almost identical-Al clusters demonstrate that results of physical measuring, e.g., of nanostructured surfaces which carry supposedly identical cluster species, have to be interpreted with great caution.
The first polyhedral aluminum subhalide Al Br ⋅20 L forms in the disproportionation of aluminum(I) bromide solutions. The cluster is built up from an Al icosahedron with ten exohedrally bound (formally divalent) Al atoms (see structure). Such a homoatomic framework is unknown for molecular compounds. Even for the element boron this framework is only found as a section from the β-rhombohedral element modification.
Multiple insertion of AlBr in bonds of AlBr3 leads to Al5Br7⋅5 THF—a new type of low‐valent aluminum halide. The actual, ionic structure of the subhalide [Al5Br6⋅6 THF]+[Al5Br8⋅4 THF]− (the anion is shown schematically) appears plausible on the basis of density functional theory calculations. This and similar subhalides can play the role of potential intermediates in the electrolytic deposition of metals.
Das erste polyedrische Aluminiumsubhalogenid Al22Br20⋅12 L entsteht bei der Disproportionierung von AlI‐Bromid‐Lösungen. Der Cluster ist aus einem Al12‐Ikosaeder mit zehn exohedral gebundenen (formal zweiwertigen) Al‐Atomen aufgebaut (siehe Struktur). Ein derartiges homoatomares Gerüst ist bei molekularen Verbindungen unbekannt. Selbst beim Element Bor findet man dieses Gerüst lediglich als Ausschnitt aus der β‐rhomboedrischen Elementmodifikation.
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