Al22Br20⋅12 THF: The First Polyhedral Aluminum Subhalide—A Step on the Path to a New Modification of Aluminum?

Abstract

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.

Experimentally Based DFT Calculations on the Hindered Disproportionation of [Al4Cp*4]: Formation of Metalloid Clusters as Intermediates on the Way to Solid Al Prevents the Decomposition of a Textbook Molecule

“…[27] metallic b-Al should have an icosahedral arrangement of the Al atoms as in a-or b-boron and should have an expanded atomic volume in comparison to metallic aluminum. [13,36] Therefore, the disproportionation of the aluminum subhalides is more complex than that of the tetrameric cyclopentadienyl derivates 1 and 2 described herein.…”

“…Behavior analogous to the disproportionation of 1 via a barrier may be valid for the subhalides AlX and Al 4 X 4 ·4L (X = Br, L = donor molecule, e.g., NEt 3 ) [33][34][35] (see the Supporting Information). However, the observation of intermediates (Al 22 X 20 ) [13,36] with a central icosahedral Al 12 core has been the basis for the hypothesis of a second nonmetallic modification of Al, which is metastable with respect to metallic Al by about 30 kJ. This so-called hypothetical non- (1)] is 941 kJ above the Al 4 Cp* 4 and 84 kJ below the Al 4 Cp 4 level.…”

Ga24Br18Se2: A Highly Symmetrical Metalloid Cluster and Its One‐Dimensional Arrangement in the Crystalline State as a Model for the Photoconductivity of Solid GaSe

“…In recent years, we succeeded in preparing two subhalides of Group XIII elements with a central M 12 icosahedron, [Al 22 Br 20 ]·12 thf (1) [1,2] and [Ga 24 Br 22 ]·10 thf (2). [3] Such neutral binary metalloid cluster molecules are unique in cluster chemistry, and they occupy an exceptional position in the group of metalloid Al and Ga clusters.…”

“…Thus, 1 and 2 could be interpreted as possible intermediates along the route to hypothetical nonmetallic modifications of aluminum or gallium (similar to a-boron). [1][2][3] Functionalization (substitution) of 1 and 2 allows us to study such defined clusters and to investigate their interactions with, for example, Au surfaces or clusters. Substitution of halogen atoms with selenium seemed expedient because of the availability of suitable precursors (e.g.…”

“…Therefore, the bonding situation is similar to that discussed for 1 and 2. [1][2][3] The GaÀ Se bond lengths vary only slightly between 2.49 and 2.50 . The GaÀO distances (to thf) vary between 1.98 and 2.00 , and the Ga À Br distances are between 2.36 and 2.38 .…”