RESUMEN
Magnesium bromide radicals have to be prepared as high-temperature molecules and trapped as a metastable solution because a seemingly simple reduction of donor-free Grignard compounds failed. However, the essential role of magnesium(I) species during the formation of Grignard compounds could be demonstrated experimentally.
RESUMEN
Because of their thermodynamic instability, their sophisticated formation, and their high reactivity, only three textbook examples of Al(I)/Ga(I) subhalides have been crystallized so far: Al(4)Br(4), Al(4)I(4), and Ga(8)I(8). Here, we present the formation and structural characterization of molecular Ga(8)Br(8) species. The different structures of Ga(8)I(8) and Ga(8)Br(8) are discussed with regard to their different formation conditions and their different thermodynamic stability based on results from DFT calculations. Structural as well as thermodynamic properties of Ga(8)I(8) and Ga(8)Br(8) are strongly related to the low-temperature modifications beta-Ga and gamma-Ga. Therefore, our fruitful hypothesis about the fundamental relation between structure and energy of a number of metalloid clusters and the corresponding element modifications is now supported by two binary Ga(I)-halide compounds.
RESUMEN
The well known thermodynamic instability of Al and Ga monohalides is caused by the favored disproportionation process to the bulk metal and the trihalides. During this highly complex process, a number of metalloid clusters that are intermediates on the way to the metal have been trapped. Therefore, all observations in the field of metalloid Al/Ga clusters have been traced to this favored disproportionation process. The failure to form phosphanide-substituted Al clusters, in contrast to the generation of similar Ga clusters and analogous Al amide clusters, was the starting point of this contribution. For aluminum(I) phosphanides, there exists a different decomposition route in which the salt-like bulk material AlP and not Al metal is the final product. The synthesis of two molecular "AlP" intermediate species, together with supporting DFT calculations, provide plausible arguments for this decomposition route, which is thermodynamically favored for many AlR/GaR species and which, surprisingly, has not been discussed before.
RESUMEN
The highly energetic molecule Al(4)H(6), with its distorted tetrahedral structure, was recently characterized via mass spectrometry and photoelectron spectroscopy investigations (Li, X.; et al. Science 2007, 315, 356). Here we present the preparation and structural investigation of the first analogous Al(4)R(6) cluster compound. In order to understand the bonding in this kind of Al(4) molecule, density functional theory and second-order Møller-Plesset perturbation theory calculations were performed. The results obtained are discussed in comparison with bonding in other Al(4) moieties, especially the aromatic bonding behavior in the dianionic planar Al(4)(2-) species (Li, X.; et al. Science 2001, 291, 859). Finally, on the basis of the results obtained for Al(4) species, a more general problem is discussed: the difference in bonding between Zintl ions and metalloid clusters.