Application Note 3: Benchtop NMR on
Paramagnetic Samples
Many organometallic complexes contain paramagnetic ions. These extend the chemical
shift range of proton spectra to hundreds of ppm. At high field, such large bandwidths
are very challenging to achieve. The Magritek Spinsolve benchtop NMR spectrometerhas a special Paramagnetic protocol designed to scan such samples. The acquisition
bandwidth is 20 kHz corresponding to 480 ppm frequency range. Since paramagnetic
ions also reduce the T1 relaxation time of the sample, the repetition time between
scans is reduced to 3 seconds resulting in faster scan times. The examples in this notedemonstrate the ability of the Paramagnetic protocol to resolve peaks which are notvisible in the standard 1D Proton protocol.

BIS(N-2’-BUTYLSALICYLICYLALDIMINATO)NICKEL(II)In order to demonstrate how paramagnetic ionscan extend the spectral range, a sample ofbis(n-2’-butylsalicylicylaldiminato)nickel(II) from athird-year chemistry teaching lab was dissolvedin CDCl3 and analysed.

Figure 1 shows the spectrum of the sample using
the 1D Proton (red spectrum) and Paramagnetic(blue line) protocols. The bandwidth of the 1DProton protocol is not sufficient to cover theentire spectral range of the sample while theParamagnetic protocol tells the full story.

Figure 1

Figure 1: 1H NMR spectrum of bis(n-2’-butylsalicylicylaldiminato)nickel(II)1D Proton (red) and Paramagnetic (blue)
dissolvedCDCl
3 using theFigure
1: 1H inNMR
spectrumof bis(n-2’-butylsalicylicylaldiminato)nickel(II)protocols. Note that the bandwidth of the 1D Proton protocol isdissolved in CDCl3 using the 1D Proton (red) and Paramagnetic (blue)
to coverthe entire spectrum of the dissolved
sample.in CDCl3 using the 1D Proton
Figureinsufficient
1: 1H NMR spectrumof bis(n-2’-butylsalicylicylaldiminato)nickel(II)protocols.
Note thatthe bandwidth of the 1D Proton
protocol is(red)and Paramagnetic
protocols.
that thebandwidthofof the1D sample.
Proton protocol is insufficient to coverinsufficientto(blue)cover
the Noteentirespectrum
thethe entire spectrum of the sample.

CophenThis example from a third-year chemistry experiment demonstrates the reaction ofCophen
2+coordinated ligands using the conversion of paramagnetic [Co(phen)3] to diamagnetic

3+
This
example3]froma third-year
chemistry
demonstrates
thediffers
reactionofcomplexes.
Figure2 shows experiment
how the chemical
shift range
dramatically[Co(phen)2+
coordinatedligands
using theconversionof cobalt
paramagnetic[Co(phen)3] to diamagnetic
between theparamagnetic
anddiamagnetic
complexes.

COPHEN
This example from a third-year chemistry
experiment demonstrates the reaction of coordinatedligands using the conversion of paramagnetic[Co(phen)3]2+ to diamagnetic [Co(phen)3]3+complexes.

Figure 2 shows how the chemical shift range
differs dramatically between the paramagnetic anddiamagnetic cobalt complexes.

Figure 2

Figure 2: NMR spectrum of diamagnetic and paramagnetic Co(phen)3 dissolvedin D2O, using the Paramagnetic protocol. Note how the chemical shift range
extends
dramaticallyfor andtheparamagnetic
paramagneticcomplex.
Spectra courtesy of Paul
Figure 2: NMR
spectrumof diamagneticCo(phen)
3 dissolved in D2O, using the Paramagnetic
S Donelly, University of Melbourne.

protocol. Note how the chemical shift range extends dramatically for the paramagnetic complex. Spectra courtesy ofPaul S Donelly, University of Melbourne.

Conclusions
Paramagnetic samples are often difficult to obtain NMR spectra from. The specially designed

CONCLUSION

Paramagnetic samples are often difficult to obtain NMR spectra from. The specially designed
Paramagnetic protocol enables the Spinsolve benchtop NMR spectrometer to resolve peaks in wide line
spectra, which cannot be resolved with standard methods.

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