Über einige Aluminiumbromid-Ether-Addukte: Strukturen in Lösung und im festen Zustand / Aluminium Bromide Ether Adducts: Structures in Solution and in the Solid State

Monoglyme forms a molecular 1:1 adduct with AlBr₃ which dissociates into the ions AlBr₂(DME)₂⁺ and AlBr₄^- in DME, CH₂Br₂ and CDCl₃ as solvents. A hexacoordinated Al center is present in the solid adduct AlBr₃·diglyme. The oxygen and bromine atoms are arranged in a meriodional configuration as shown by X-ray crystallography. However, in solution dissociation occurs into AlBr₂(diglym)₂⁺ and AlBr₄^-. Not unexpectedly, AlBr₃ forms the adduct AlBr₃·2THF with tetrahydrofuran. The dioxane adduct AlBr₃·diox is polymeric in the solid state and has a chain structure with pentacoordinated trigonal-bipyramidal Al centers. The Br atoms are arranged in a slightly distorted trigonal plane. In solution, the presence of tetracoordinated Al is indicated by ²⁷AI NMR spectroscopy. AlBr₃ cleaves one of the C-O bonds of 12-crown-4 leading to the dimer of ω-bromo-tetra(ethyleneoxy)aluminium dibromide. This dimer contains pentacoordinated Al centers as proven by X-ray structure analysis. In contrast, the adduct of AlBr₃ with 15-crown-5 is most likely an ionic compound, and is best described as [AlBr₂(15-crown-5)]AlBr₄ based on ²⁷Al NMR and IR data.