The controlled disproportionation of metastable Al I halide solutions has been developed into a fruitful concept for the generation of metalloid Al cluster compounds as intermediates on the way to bulk phases of Al metal during the last years [Eq. (1), X = Cl, Br, I]. [1] 3 AlX ! 2 Al metal þ AlX 3 ð1Þ

The photoinduced reaction of AlCp* [Cp* = C5(CH3)5] monomers with H2 in an Ar matrix at 12 K was followed with IR spectroscopy. The experimental results allied with detailed quantum chemical calculations show that the product of this reaction is the new aluminum hydride species H2AlCp*. The properties of this species are investigated and compared with those of related known monomeric hydrides such as AlH3, H2AlNH2, and HAlCl2. The comparison between the reactivities of species such as AlCl and AlCp* is of importance for a better understanding of the bonding properties in AlCp*. The possibility for π-back-donation in the product of the reaction between AlCp* and H2, H2AlCp*, certainly affects chemical properties such as the Lewis acidity. The differences between the wavenumbers for the ν(Al−H) stretching modes of H2AlCp* and H2AlCl show that the influence of the Cp* group is significant.

Dedicated to Professor Peter Paetzold on the occasion of his 70th birthdayTwo subgroups of Al-metal clusters with a predominant number of metal-metal bonds are known: [1] "naked" metalatom clusters, which are produced from solid metal by laser ablation techniques, and metalloid clusters, which are formed in solution starting with Al I species and, for example, subsequent reduction. [2,3] Here we present Al 20 Cp * 8 Br 10 (1) and Al 20 Cp * 8 Cl 10 (2) (Cp* = pentamethylcyclopentadienyl), two compounds of molecular, partially substituted subhalides belonging to the second group, which at first glance seem related to the species Al 13 I x À [4] and Al 14 I x À [5] (x = 1-12), which were generated in mass-spectrometric experiments. In both sets of compounds the halogen atoms form direct bonds to the Al atoms of the icosahedral Al 12 cluster core. However, quantum-chemical calculations for "naked" anionic clusters, for example, the Al 13 I x À anion mentioned above, indicate that an additional Al atom is located in the center.The structures of 1 and 2 are furthermore closely related to those of the recently characterized Al 22 X 20 compounds (X = Cl, Br), for example, Al 22 Br 20 (3) [6] because their cluster

Die kontrollierte Disproportionierung von metastabilen AlIHalogenid-Lösungen hat sich in den letzten Jahren zu einer erfolgreichen Strategie für die Herstellung von metalloiden Al-Clusterverbindungen als Zwischenstufen auf dem Weg zu Aluminiummetall-Volumenphasen entwickelt [Gl. (1), X = Cl, Br, I]. [1] 3 AlX ! 2 Al metal þ AlX 3 ð1ÞUm die thermodynamisch bevorzugte Metallbildung zu verhindern, werden die Halogenidliganden -parallel zur Disproportionierungsreaktion -durch sperrige Liganden substituiert. Die Mehrzahl der metalloiden Al-Cluster, die in unserer Arbeitsgruppe hergestellt wurden, ist durch N(SiMe 3 ) 2 -Liganden geschützt.[1] Hier stellen wir einen großen metalloiden Al-Cluster vor, der ausschließlich aus Al-, C-und H-Atomen aufgebaut ist.

The structure of bis(pentamethylcyclopentadienyl)magnesium, Mg(C 5 Me 5 ) 2 ( 1), in the solid state has been determined by X-ray diffraction. The experimental results are described and discussed in comparison to structural properties of the higher alkaline-earth metallocenes MCp* 2 (M ) Ca, Sr, Ba) as determined in the gas phase or in the solid state. Structural trends of 1 in comparison to the isoelectronic species [LiCp* 2 ] -, BeCp* 2 , and [AlCp* 2 ] + are also presented.