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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

Properties of ⁶⁹Ga

(Click here for explanation)

Property	Value
Spin	3/2
Natural abundance	60.108%
Chemical shift range	1436 ppm, from -706 to 730
Frequency ratio (Ξ)	24.001354%
Reference compound	Ga(NO3)3 in D2O
Linewidth of reference	1002 Hz
T1 of reference	0.00026 s
Receptivity rel. to 1H at natural abundance	0.0419
Receptivity rel. to 1H when enriched	0.0697
Receptivity rel. to 13C at natural abundance	246
Receptivity rel. to 13C when enriched	409
Linewidth parameter	390 fm4

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

Properties of ⁷¹Ga

(Click here for explanation)

Property	Value
Spin	3/2
Natural abundance	30.83%
Chemical shift range	1436 ppm, from -706 to 730
Frequency ratio (Ξ)	30.496704%
Reference compound	Ga(NO3)3 in D2O
Linewidth of reference	407 Hz
T1 of reference	0.00074 s
Receptivity rel. to 1H at natural abundance	0.0517
Receptivity rel. to 1H when enriched	0.185
Receptivity rel. to 13C at natural abundance	335
Receptivity rel. to 13C when enriched	1087
Linewidth parameter	150 fm4

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.

References

• 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).
• 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).