Safety note: Some of the materials mentioned here are very dangerous. Ask a qualified chemist for advice before handling them. Qualified chemists should check the relevant safety literature before handling or giving advice about unfamiliar substances. NMR solvents are toxic and most are flammable. Specifically, gallium nitrate is an oxidant and irritant and other gallium salts may be corrosive and react violently with water.

Gallium NMR

Gallium (Ga) has two NMR active nuclei, ⁶⁹Ga and ⁷¹Ga (fig. 1) with a very wide chemical shift range (fig. 2). Both nuclei are quadrupolar and therefore yield broad signals in small molecules and signals, too broad to be observed with a high-resolution NMR spectrometer, in medium and large molecules. ⁷¹Ga is the more sensitive nucleus and yields narrower signals than ⁶⁹Ga so ⁷¹Ga is the nucleus of choice unless studying isotopic enrichment.

Fig. 1. Comparison of ⁶⁹Ga and ⁷¹Ga for Ga(NO₃)₃ in D₂O. ⁷¹Ga is the more sensitive nucleus and yields narrower signals.

Fig. 2. Chemical shift ranges for gallium NMR

Each type of gallium compound has its characteristic chemical shift range (fig. 2). Note that aqueous solutions of gallium salts are usually hexacoordinated to water.

⁶⁹Gallium NMR

⁶⁹Ga (fig. 3) is less sensitive and yields broader signals than ⁷¹Ga so it is not the nucleus of choice except potentially for certain isotopic enrichment studies.

Fig. 3. ⁶⁹Ga-NMR spectrum of Ga(NO₃)₃ (1.1 m) in D₂O

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Properties of ⁶⁹Ga

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⁷¹Gallium NMR

⁷¹Ga (fig. 4) is the gallium nucleus of choice as it is more sensitive and yields narrower signals than ⁶⁹Ga.

Fig. 4. ⁷¹Ga-NMR spectrum of Ga(NO₃)₃ (1.1 m) in D₂O

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Properties of ⁷¹Ga

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References

1. B. R. McGarvey, M. J. Taylor and D. G. Tuck, "Gallium-71 NMR studies of anionic gallium halide species in nonaqueous solution" Inorg. Chem., 20, 2010-2013 (1981).
2. Z. Cerny, J. Machacek, J. Fusek,O. Kriz, B. Casensky, D. G. Tuck, "⁷¹Ga NMR studies of mixtures of gallium trichloride and trimethylgallium" J. Organometal. Chem., 456, 25-30 (1993).

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