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A justification for using NMR model‐free methods when investigating the solution structures of rhombic paramagnetic lanthanide complexes
Author(s) -
Terazzi Emmanuel,
Rivera JeanPierre,
Ouali Nadjet,
Piguet Claude
Publication year - 2006
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1790
Subject(s) - paramagnetism , isostructural , lanthanide , chemistry , hyperfine structure , anisotropy , crystallography , crystal structure , condensed matter physics , physics , ion , atomic physics , organic chemistry , quantum mechanics
The detailed analysis of the 1 H NMR hyperfine shifts according to the model‐free methods shows that the semi‐rigid monometallic complexes [Ln(L)(NO 3 ) 3 ] (Ln = Eu–Yb) are isostructural in solution. The associated separation of contact and pseudo‐contact contributions to the hyperfine NMR shifts in each rhombic lanthanide complex at room temperature provides paramagnetic susceptibility tensors whose principal magnetic axes match the expected symmetry requirements. Moreover, both axial (Δχ ax ) and rhombic (Δχ rh ) paramagnetic anisotropies display satisfactory linear dependence on Bleaney's factors, a correlation predicted by the approximate high‐temperature expansion of the magnetic susceptibility limited to T −2 . Consequently, the simple, and chemically attracting NMR model‐free methods are not limited to axial systems, and can be safely used for the investigation of the solution structures of any lanthanide complexes. Molecular‐based structural criteria for the reliable estimation of paramagnetic susceptibility tensors by NMR are discussed, together with the assignment of the labels of the crystal‐field and magnetic axes within Bleaney's approach. Copyright © 2006 John Wiley & Sons, Ltd.