[en] Bromine-81 and aluminum-27 nuclear quadrupole resonance (NQR) data have been obtained for a series of MAl₂Br₇ compounds (M = NH₄, (CH₃)₄N, and (C₂H₅)₄N). For the cation change from (C₂H₅)₄N⁺ to NH₄⁺, the bridging ⁸¹Br NQR frequency increases about 10 MHz, which is about 13% of that in the (C₂H₅)₄NAl₂Br₇ compound and too large to arise from only crystal field effects. This large frequency shift is suggestive of the polarization of the anion induced by neighboring cations. That is, the negative charges of the anion are more localized at the terminal positions than at the bridging position with increasing polarizing power of the cation. The nuclear quadrupole coupling constants of ²⁷Al increase with increasing cation radius. This finding also supports the anion polarization model. 18 references, 3 figures, 2 tables