NQR Study of AlBr3 Complexes with Donor-Acceptor O-Al Bond

Abstract

Abstract 81Br and 27Al NQR were observed in AlBr 3 complexes with 4-XC6H4 NO,(X = H, CI, Br, I, CH3 , and C2H5), C6H5COBr, (C6H5)2CO, and (C2H5)2O. In the 4-XC6H4 NO2 complexes, the 27Al quadrupole coupling constants (QCC's) were well correlated with the Hammett er p 's of the para-substituents, i.e., electron-withdrawing groups caused reduction of the charge density of O-Al bonds which resulted in large 27Al QCC's and vice versa. The temperature dependences of the 81Br NQR frequencies and quadrupolar spin-lattice relaxation times showed that the 4-C2H5C6H4NO2 and C6H5 COBr complexes undergo phase transitions at 154 K and around 200 K, respectively, and show hindered rotation of the AlBr3 groups at higher temperatures, and that the (C2H5) 2O complex reorients above ca. 120 K.