Multiple-magnetic field 139La NMR and density functional theory investigation of the solid lanthanum(III) halides

Results from a solid-state La-139 NMR spectroscopic investigation of the anhydrous lanthanum(III) halides (LaX3; X = F, Cl, Br, 1) at applied magnetic fields of 7.0, 9.4, 11.7, 14. 1, and 17.6 T are presented and highlight the advantages of working at high applied magnetic field strengths. The La-139 quadrupolar coupling constants are found to range from 15.55 to 24.0 MHz for LaCl3 and Lab, respectively. The lanthanum isotropic chemical shifts exhibit an inverse halogen dependence with values ranging from -135 ppm for LaF3 to 700ppm for Lab, which represents nearly half of the total lanthanum chemical shift range. The spans of the magnetic shielding tensors also vary widely, from 35 to 650 ppm for the solid LaF3 through LaI3. DIFT calculations of the 139La electric field gradient and magnetic shielding tensors have been performed and provide a qualitative interpretation of the trends observed experimentally. (c) 2005 Elsevier Inc. All rights reserved.