Solid‐state NMR characterization of 69Ga and 71Ga in crystalline solids

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Abstract
Gallium model systems containing four‐ and six‐coordinate gallium sites have been investigated using solid‐state NMR. Measurement of the isotropic chemical shift and electric field gradient (EFG) have been performed at 9.4 T on α‐Ga2O3, β‐Ga2O3, LiGaO2, NaGaO2, KGaO2, Ga2(SO4)3, and LaGaO3 using a variety of techniques on both NMR active nuclei (69Ga and 71Ga) including static, high speed magic‐angle spinning (MAS), satellite transition (ST) spectroscopy, and rotor‐assisted population transfer (RAPT). The chemical shift is found to correlate well with the coordination number, with four‐coordinate gallium having values of approximately 50 ppm and six‐coordinate gallium having values near 225 ppm (referenced to 1 M gallium nitrate solution). The magnitude of the EFG is found to be correlated to the distortion of the gallium polyhedra, with the strained systems having EFGs of 3 × 1021 Vm−2 or more, while the less strained systems have values of 1.5 × 1021 Vm−2 or less. A plot of chemical shift versus EFG suggests that solid‐state NMR of gallium oxyanions can be more discriminating than liquid state NMR chemical shifts alone. Copyright © 2006 John Wiley & Sons, Ltd.

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