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Copper (Cu) has two NMR active nuclei, ⁶³Cu and ⁶⁵Cu with a very wide chemical shift range (fig. 1). 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. ⁶³Cu is the more sensitive nucleus while ⁶⁵Cu yields very slightly narrower signals (fig. 2). Usually though ⁶³Cu NMR is preferred.

Fig. 1. Chemical shift ranges for copper NMR

Fig. 2. Comparison of ⁶³Cu and ⁶⁵Cu for CuCl in CD₃CN. ⁶³Cu yields greater sensitivity while ⁶⁵Cu yields marginally narrower signals.

Each type of copper complex has its characteristic chemical shift range (fig. 1). Copper NMR is only observed for oxidation state (I) because (II) is paramagnetic.

⁶³Copper NMR

⁶³Cu (fig. 3) is usually the nucleus of choice since it is more sensitive than ⁶⁵Cu even though it yields marginally broader signals.

Fig. 3. ⁶³Cu-NMR spectrum of CuCl in CD₃CN

Properties of ⁶³Cu

(Click here for explanation)

Property	Value
Spin	3/2
Natural abundance	69.7%
Chemical shift range	1100 ppm, from -300 to 800
Frequency ratio (Ξ)	26.515473%
Reference compound	[Cu(CH3CN)4][ClO4] + 10% C6D6
Linewidth of reference	400 Hz
T1 of reference	0.0004 s
Receptivity rel. to 1H at natural abundance	0.0650
Receptivity rel. to 1H when enriched	0.0940
Receptivity rel. to 13C at natural abundance	382
Receptivity rel. to 13C when enriched	552
Linewidth parameter	650 fm4

⁶⁵Copper NMR

⁶⁵Cu (fig. 4) is less sensitive than ⁶³Cu even though it yields marginally narrower signals. ⁶⁵Cu would only be the nucleus of choice for isotopic enrichment studies or in the unlikely event that resolution is critical.

Fig. 4. ⁶⁵Cu-NMR spectrum of CuCl in CD₃CN

Properties of ⁶⁵Cu

(Click here for explanation)

Property	Value
Spin	3/2
Natural abundance	30.83%
Chemical shift range	1100 ppm, from -300 to 800
Frequency ratio (Ξ)	28.403693%
Reference compound	[Cu(CH3CN)4][ClO4] + 10% C6D6
Linewidth of reference	400 Hz
T1 of reference	0.0004 s
Receptivity rel. to 1H at natural abundance	0.0354
Receptivity rel. to 1H when enriched	0.115
Receptivity rel. to 13C at natural abundance	208
Receptivity rel. to 13C when enriched	675
Linewidth parameter	550 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, copper salts are toxic.