Multinuclear NMR studies of mixtures of aluminium and gallium trihalides in benzene

Abstract

The ²⁷Al and ⁷¹Ga NMR spectra of mixtures of M₂X₆ and M₂Y₆ (M = Al, Ga; X ≠ Y = Cl, Br or I) in benzene are reported. All these systems show rapid inter-halogen exchange, and in some cases stable intermediates M₂X_nY_6 − n can be characterised spectroscopically. In particular, the results are used to identify the predominant species present in solutions prepared by mixing (i) Al₂Br₆ and Ga₂Cl₆, and (ii) Al₂I₆ and Ga₂Br₆, in benzene in various mole ratios. The expected M₂X₃Y₃ intermediates are found for M = Al or Ga, X ≠ Y = Cl, Br, but with other mixed halide systems, unsymmetric structures predominate, and possible reasons for this are discussed. The experimental results are in agreement with thermodynamic predictions, and with arguments based on maximizing the M–X, Y electronegativity differences.