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Rhenium (Re) has two medium sensitivity NMR active nuclei, ¹⁸⁵Re and ¹⁸⁷Re. ¹⁸⁷Re is more sensitive and yields less broad signals than ¹⁸⁵Re (fig. 1). ¹⁸⁷Re is therefore the preferred rhenium nucleus as. Both nuclei are quadrupolar and yield extremely broad signals even for small molecules in symmetric environments. There is no information regarding chemical shifts of rhenium. As a result rhenium NMR is hardly used. Rhenium is one of the rare cases when both nuclei have frequencies close enough that they can be observed in the same spectrum using a high-resolution spectrometer (fig. 2).

Fig. 1. Comparison of ¹⁸⁵Re and ¹⁸⁷Re NMR for ND₄ReO₄ (0.1 M) in D₂O

Fig. 2. Both isotopes of rhenium in the same spectrum

¹⁸⁵Rhenium NMR

¹⁸⁵Re (fig. 3) yields signals that are less sensitive and broader than ¹⁸⁷Re. Therefore ¹⁸⁷Re NMR is the preferred rhenium nucleus.

Fig. 3. ¹⁸⁵Re NMR for ND₄ReO₄ (0.1 M) in D₂O

Properties of ¹⁸⁵Re

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Property	Value
Spin	5/2
Natural abundance	37.40%
Chemical shift range	Unknown
Frequency ratio (Ξ)	22.524600%
Reference compound	0.1 M KReO4 in D2O
Linewidth of reference	11000 Hz
T1 of reference	0.00002 s
Receptivity rel. to 1H at natural abundance	0.0519
Receptivity rel. to 1H when enriched	0.139
Receptivity rel. to 13C at natural abundance	305
Receptivity rel. to 13C when enriched	816
Linewidth parameter	15000 fm4

¹⁸⁷Rhenium NMR

¹⁸⁷Re (fig. 4) yields signals that are more sensitive and less broad than ¹⁸⁵Re. Therefore ¹⁸⁷Re NMR is the preferred rhenium nucleus.

Fig. 4. ¹⁸⁷Re NMR for ND₄ReO₄ (0.1 M) in D₂O

Properties of ¹⁸⁷Re

(Click here for explanation)

Property	Value
Spin	5/2
Natural abundance	62.60%
Chemical shift range	Unknown
Frequency ratio (Ξ)	22.751600%
Reference compound	0.1 M KReO4 in D2O
Linewidth of reference	9000 Hz
T1 of reference	0.00002 s
Receptivity rel. to 1H at natural abundance	0.0895
Receptivity rel. to 1H when enriched	0.143
Receptivity rel. to 13C at natural abundance	526
Receptivity rel. to 13C when enriched	840
Linewidth parameter	14000 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, rhenium salts may be toxic.

References

• R. A. Dwek, Z. Luz and M. Shporer, "Nuclear Magnetic Resonance of Aqueous Solutions of Sodium Perrhenate", J. Phys. Chem., 74, 2232-2233 (1970).