Magnetic anisotropy of endohedral lanthanide ions: paramagnetic NMR study of MScN@C- with M running through the whole 4f row.

Paramagnetic and variable temperature C and Sc nuclear magnetic resonance studies are performed for nitride clusterfullerenes MScN@C with icosahedral (7) carbon cage, where M runs through all lanthanides forming nitride clusters. The influence of the endohedral lanthanide ions on the NMR spectral pattern is carefully followed, and dramatic differences are found in peak positions and line widths. Thus, C lines broaden from 0.01-0.02 ppm in diamagnetic MScN@C molecules (M = La, Y, Lu) to several ppm in TbScN@C and DyScN@C. Direction of the paramagnetic shift depends on the shape of the 4f electron density in corresponding lanthanide ions. In TmScN@C and ErScN@C with prolate 4f-density of lanthanide ions, C signals are shifted down-field, whereas Sc peaks are shifted up-field diamagnetic values. In all other MScN@C molecules lanthanide ions have oblate-shaped 4f electron density, and the lanthanide-induced shift is negative for C and positive for Sc peaks. Analysis of the pseudocontact and contact contributions to chemical shifts revealed that the pseudocontact term dominates both in C and Sc NMR spectra, although contact shifts for C signals are also considerable. Point charge computations of the ligand field splitting are performed to explain experimental results, and showed reasonable agreement with experimental pseudocontact shifts. Nitrogen atom bearing large negative charge and located close to the lanthanide ion results in large magnetic anisotropy of lanthanide ions in nitride clusterfullerenes with quasi-uniaxial ligand field.