ALUMINUM COMPLEXES IN SOLUTION AS STUDIED BY ALUMINUM-27 NUCLEAR MAGNETIC RESONANCE

Aluminum-27 magnetic resonance of various aluminum complexes has been observed in solution. Aluminum-27 in octahedral complexes shows chemical shifts about 100 ppm higher than 27Al in tetrahedral complexes. Each type of complex shows a slightly different chemical shift depending upon ligand atoms directly bonded to the metal. Iodo complexes of the type AlL4 are exceptional, showing chemical shifts similar to octahedral complexes. Mixed complexes of the type AlX3L (X = Cl, Br; L = (C2H5)2O, C6H6) give signals at fields intermediate between octahedral and tetrahedral ones. The line widths are mainly determined by the quadrupole interactions and reflect the symmetry of complexes in solution. Chemical shifts are used along with line widths to identify the chemical species produced by dissolving anhydrous aluminum halides in various organic solvents. In addition, a sequence of the affinities of the ligands to the aluminum ion has been determined as follows: H2O > C2H5OH, C3H7OH ≫ Cl, Br, I ≳ C2H5NCS > C6H5CN > CH2=CHCN > CH3CN.