Synthesis and structure of metalloid aluminum clusters—intermediates on the way to the elements

Abstract Metastable Aluminum(I) halide solutions proved to have a high potential for the synthesis of novel subvalent Al compounds, such as Al n X m species (X=Cl, Br, I; n m , average oxidation state of Al below +3 or n > m , average oxidation state of Al below +1) or Al n R m species (R=bulky ligand; n > m ). There are two principal reaction types, which are essential for the formation of the compounds discussed herein. The disproportionation, which finally results in Al(III) halides and Al metal and the metathesis which leads to a substitution of X atoms against R groups. By this way the metalloid cluster compounds [Al 7 {N(SiMe 3 ) 2 } 6 ] − , [Al 12 {N(SiMe 3 ) 2 } 8 ] − , [Al 14 I 6 {N(SiMe 3 ) 2 } 6 ] 2− , [Al 69 {N(SiMe 3 ) 2 } 18 ] 3− , and [Al 77 {N(SiMe 3 ) 2 } 20 ] 2− could be isolated. The characteristic feature of these metalloid Al clusters is the number of AlAl contacts being larger than the number of Alligand bonds, i.e. there are more ‘naked’ than ligand-bonded Al atoms. Furthermore, the topology of the closest packing in Al metal is already pre-formed in these compounds.