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Indium (In) has two NMR active nuclei that have a very wide chemical shift range. ¹¹³In and ¹¹⁵In, are both quadrupolar and yield extremely broad lines even in small symmetrical ions. ¹¹⁵In is preferred as it has the higher sensitivity and yields very slightly narrower signals than ¹¹³In (fig. 1). Indium NMR has limited use used for the study of solvated indium ions or molten salts. Indium is unusual in that their resonant frequency difference is a little over 2000 ppm so both nuclei can be observed at the same time (fig. 1).

Fig. 1. Comparison of the indium isotopes ¹¹³In on the right (upper scale) and ¹¹⁵In on the left (lower scale) for In(NO₃)₃ in nitric acid/D₂O

Both the isotopes have the same chemical shifts (fig. 2).

Fig. 2. Chemical shift ranges for indium NMR

¹¹³Indium NMR

(¹¹³In) ¹¹³Indium is a spin 9/2 nucleus and is therefore quadrupolar. As a result, the signal width is very broad for small symmetrical ions and increases with asymmetry of the environment (fig. 3). ¹¹³In is less sensitive and yields marginally broader signals than ¹¹⁵In so ¹¹⁵In is the nucleus of choice for indium NMR unless studying isotopic enrichment.

Fig. 3. ¹¹³In-NMR spectrum of In(NO₃)₃ in nitric acid/D₂O

Properties of ¹¹³In

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Property	Value
Spin	9/2
Natural abundance	4.29%
Chemical shift range	1100 ppm, from -500 to 600
Frequency ratio (Ξ)	21.865755%
Reference compound	In(NO3)3 (0.1 M) in dilute HNO3
Linewidth of reference	4314 Hz
T1 of reference	50 µs
Receptivity rel. to 1H at natural abundance	0.0151
Receptivity rel. to 1H when enriched	0.352
Receptivity rel. to 13C at natural abundance	88.5
Receptivity rel. to 13C when enriched	2063
Linewidth parameter	470 fm4

¹¹⁵Indium NMR

(¹¹⁵In) ¹¹⁵Indium is a spin 9/2 nucleus and is therefore quadrupolar. As a result, the signal width is very broad for small symmetrical ions and increases with asymmetry of the environment (fig. 4). ¹¹⁵In is more sensitive and yields marginally less broad lines than ¹¹³In so ¹¹⁵In is the indium nucleus of choice.

Fig. 4. ¹¹⁵In-NMR spectrum of In(NO₃)₃ in nitric acid/D₂O

Properties of ¹¹⁵In

(Click here for explanation)

Property	Value
Spin	9/2
Natural abundance	95.71%
Chemical shift range	1100 ppm, from -500 to 600
Frequency ratio (Ξ)	21.912629%
Reference compound	In(NO3)3 (0.1 M) in dilute HNO3
Linewidth of reference	4263 Hz
T1 of reference	50 µs
Receptivity rel. to 1H at natural abundance	0.338
Receptivity rel. to 1H when enriched	0.353
Receptivity rel. to 13C at natural abundance	1980
Receptivity rel. to 13C when enriched	2069
Linewidth parameter	490 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, indium salts may be toxic.