Ring and cage compounds from complexes of group 13 metal halides with ethylenediamine: Experiment and theory

Formation of gaseous ring and cage compounds by thermolysis of the complexes between group 13 metal halides MX₃ and ethylenediamine (en) has been observed experimentally by mass spectrometry method (M = Al, Ga; X = Cl, Br, I) and studied theoretically. Existence of gaseous associates with molecular weight of 600-900 amu was observed for all studied systems. The abundance of the high molecular weight species decreases in order AlBr₃ > AlI₃ > GaCl₃ > GaBr₃. For aluminum compounds, formation of carbon-free cubane-type clusters was evidenced. Theoretical ab initio studies at B3LYP/LANL2DZ(d,p) level of theory have been performed for the series of the ring and cage oligomer compounds in Al₂Br₆-en system. A mechanistic pathway of the formation of inorganic rings and cages by subsequent HBr elimination and oligomerization reactions has been proposed. It is concluded that elimination reactions take place in the condensed phase.