(V) Vanadium NMR

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Vanadium (V) has two NMR active nuclei, ⁵⁰V and ⁵¹V, with a very wide chemical shift range (fig. 1). Both nuclei are quadrupolar and therefore yield relatively broad signals in small molecules and signals, too broad to be observed with a high-resolution NMR spectrometer, in large molecules. ⁵¹V is the nucleus of choice because it is by far the more sensitive and yields much narrower lines although this is only relative and ⁵¹V signals are quite broad (fig. 2). Vanadium NMR is used in the study of small vanadium complexes and vanadium binding in solution.

Fig. 1. Chemical shift ranges for vanadium NMR

Fig. 2. Comparison of ⁵⁰V and ⁵¹V for VOCl₃ (neat). ⁵¹V yields much greater sensitivity and much narrower signals.

Each type of vanadium compound has its characteristic chemical shift range (fig. 1). The NMR of Vanadium can be observed in its (-I), (I), and (V) oxidation states however, V(0), (II) and (IV) are paramagnetic and cannot be observed in high resolution NMR.

⁵⁰Vanadium NMR

⁵⁰V (fig. 3) is much less sensitive and yields much broader signals than ⁵¹V so is not the nucleus of choice.

Fig. 3. ⁵⁰V-NMR spectrum of neat VOCl₃

Properties of ⁵⁰V

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Property	Value
Spin	6
Natural abundance	0.250%
Chemical shift range	1900 ppm, from -1900 to 0
Frequency ratio (Ξ)	9.970309%
Reference compound	VOCl3 (90%) in C6D6*
Linewidth of reference	68 Hz
T1 of reference	0.005 s
Receptivity rel. to 1H at natural abundance	1.39 × 10-4
Receptivity rel. to 1H when enriched	0.0556
Receptivity rel. to 13C at natural abundance	0.818
Receptivity rel. to 13C when enriched	327
Linewidth parameter	17 fm4

*Note that pure VOCl₃ resonates at 2 ppm in the ⁵⁰V-NMR spectrum.

⁵¹Vanadium NMR

⁵¹V preferred as an NMR nucleus over ⁵⁰V because it is much more sensitive and yields shaper signals. ⁵¹V yields somewhat broad lines in small symmetric molecules (fig. 4) but its signals become wider with increasing size of the complex and too broad to observe with a high-resolution NMR spectrometer for medium sized complexes. ⁵¹V NMR is used in the study of small vanadium complexes and vanadium binding in solution.

Fig. 4. ⁵¹V-NMR spectrum of neat VOCl₃

Properties of ⁵¹V

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Linewidth parameter

Property	Value
Spin	7/2
Natural abundance	99.750%
Chemical shift range	1900 ppm, from -1900 to 0
Frequency ratio (Ξ)	26.302948%
Reference compound	VOCl3 (90%) in C6D6
Linewidth of reference	21 Hz
T1 of reference	0.0203 s
Receptivity rel. to 1H at natural abundance	0.383
Receptivity rel. to 1H when enriched	0.384
Receptivity rel. to 13C at natural abundance	2250
Receptivity rel. to 13C when enriched	2256
3.7 fm4

*Note that pure VOCl₃ resonates at 2 ppm in the ⁵¹V-NMR spectrum.

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, VOCl3 is toxic and reacts with moist air to give toxic fumes (HCl): wear gloves, work under nitrogen in a hood. Vanadium salts are toxic: wear gloves. ⁵⁰V is very slightly radioactive but is not considered a radiation hazard, at least at natural abundance.