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Detailed analysis of the 1H NMR spectra of paramagnetic 10-coordinated lanthanide(III) complexes, performed with the aid of density functional theory calculations, allowed a reliable separation of the contact and pseudocontact contributions to the observed paramagnetic shifts. Analysis of the pseudocontact shifts reveals magnetic anisotropies that do not follow the trends predicted by the theory developed by Bleaney.
We report a complete set of magnetic susceptibilities of lanthanide complexes with a macrocyclic ligand based on a 3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane platform containing four hydroxyethyl pendant arms (L1). The [LnL1]3+ complexes are isostructural along the lanthanide series from Ce3+ to Yb3+, with the only structural change observed along the series being the monotonous shortening of the Ln–donor distances due to lanthanide contraction. The 1H NMR spectra point to a D2 symmetry of the [LnL1]3+ complexes in aqueous solution, which provides a unique opportunity for analysis of the rhombic magnetic anisotropies with an unequivocal location of the magnetic axes. The contact contributions for the observed paramagnetic shifts have been estimated with density functional theory calculations on the [GdL1]3+ complex. Subsequently, the pseudocontact shifts could be factored out, thereby giving access to the axial and rhombic contributions of the magnetic susceptibility tensor. Our results show that the calculated magnetic anisotropies do not follow the trends predicted by Bleaney’s theory, particularly in the case of Ho3+ and Er3+ complexes.
|حجم فایل||950 B|