There is a large contact term contribution to 13C paramagnetic shifts induced by Eu(dpm),, Pr(dpm),, and Eu(fod), in pyridine and p-picoline ; this contribution may not be due mainly to spin delocalization through n-bonds.ALTHOUGH it is generally accepted that paramagnetic shifts induced by some lanthanide complexes are mainly due to pseudo-contact interactioql it has been recently reported that abnormal shift values are observed for atoms (14N), co-ordinated to the lanthanide ion2 and for 13C or lH nuclei close to the co-ordinating atom in some aliphatic corn pound^.^ Johnson et al. have reported that abnormal relative lH shift patterns are observed for substituted pyridine N-oxides and anilines with some lanthanide complexes, and that the shift patterns for these substrates with Eu(fod), are characteristic of a contact interaction attributed to n-spin density.4 For pyridine derivatives, the observed shifts induced by La(dpm), (La = Pr, Eu, and Yb) could be interpreted approximately in terms of a pseudo-contact interaction only by using a distance between nitrogen and lanthanide ion of 4 k 5 Huber et al. tenta-31.
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