Two-dimensional solid state nmr and separation of ⁷Li quadrupolar interactions in paramagnetic compounds

Abstract

In layered paramagnetic compounds, such as La₂Li_0.5Ni_0.5O₄ with a perovskite structure, the ⁷Li NMR spectrum is broadened by anisotropic quadrupolar as well as paramagnetic dipolar interactions. We have used a two-dimensional spin echo (SE) experiment to separate the quadrupolar interaction and obtain a clean quadrupolar spectrum along the ω₁ dimension. This is demonstrated in La₂Li_0.5B_0.5O₄ (B = Cu, Ni), through 2D SE experiments conducted in static samples as well as those in spinning at the magic angle. A quadrupole coupling constant of 92 kHz is estimated from the ω₁ spectrum for paramagnetic La₂Li_0.5Ni_0.5O₄.