Lanthanide induced shifts and relaxation rate enhancements

Chemical shifts present crucial information about an NMR spectrum They show the influence of the chemical environment on the nuclei being probed Relativistic effects caused by the presence of an 

Relativistic Heavy-Neighbor-Atom Effects on NMR Shifts: Concepts and Trends Across the Periodic Table

Complexes of lanthanide(III) ions are being actively studied because of their unique ground and excited state properties and the associated optical and magnetic behavior. In particular, they are used as emissive probes in optical spectroscopy and microscopy and as contrast agents in magnetic resonance imaging (MRI). However, the design of new complexes with specific optical and magnetic properties requires a thorough understanding of the correlation between molecular structure and electric and magnetic susceptibilities, as well as their anisotropies. The traditional Judd-Ofelt-Mason theory has failed to offer useful guidelines for systematic design of emissive lanthanide optical probes. Similarly, Bleaney's theory of magnetic anisotropy and its modifications fail to provide accurate detail that permits new paramagnetic shift reagents to be designed rather than discovered.A key determinant of optical and magnetic behavior in f-element compounds is the ligand field, often considered as an electrostatic field at the lanthanide created by the ligands. The resulting energy level splitting is a sensitive function of several factors: the nature and polarizability of the whole ligand and its donor atoms; the geometric details of the coordination polyhedron; the presence and extent of solvent interactions; specific hydrogen bonding effects on donor atoms and the degree of supramolecular order in the system. The relative importance of these factors can vary widely for different lanthanide ions and ligands. For nuclear magnetic properties, it is both the ligand field splitting and the magnetic susceptibility tensor, notably its anisotropy, that determine paramagnetic shifts and nuclear relaxation enhancement.We review the factors that control the ligand field in lanthanide complexes and link these to aspects of their utility in magnetic resonance and optical emission spectroscopy and imaging. We examine recent progress in this area particularly in the theory of paramagnetic chemical shift and relaxation enhancement, where some long-neglected effects of zero-field splitting, magnetic susceptibility anisotropy, and spatial distribution of lanthanide tags have been accommodated in an elegant way.

How the Ligand Field in Lanthanide Coordination Complexes Determines Magnetic Susceptibility Anisotropy, Paramagnetic NMR Shift, and Relaxation Behavior.

NMR analyses of molecular conformations and conformational equilibria with the lanthanide probe method

The dependence of the room-temperature magnetic anisotropy Δχ of lanthanide complexes on the type of the coordination polyhedron and on the nature of the lanthanide ion is quantitatively analyzed in terms of a model approach based on numerical calculations. The aim of this study is to establish general regularities in the variation of the sign and magnitude of the magnetic anisotropy of lanthanide complexes at room-temperature and to estimate its maximal value. Except for some special cases, the variation of the sign of the magnetic anisotropy over the series of isostructural lanthanide complexes is found to obey a general sign rule, according to which Ce(III), Pr(III), Nd(III), Sm(III), Tb(III), Dy(III), and Ho(III) complexes have one sign of Δχ and Eu(III), Er(III), Tm(III), and Yb(III) complexes have the opposite sign. Depending on the specific coordination polyhedron, a maximal magnetic anisotropy is observed for Tb(III), Dy(III), or Tm(III) complexes, and its absolute value can reach 50 000×10−6 cm3 ...

Room-temperature magnetic anisotropy of lanthanide complexes: A model study for various coordination polyhedra

The pseudocontact N.M.R. shifts due to complexes of lanthanide ions are considered in a crystal field theoretical framework including all the states J, M of an L-S manifold and an arbitrary set of crystal field parameters. Deviations from Bleaney's earlier theory are shown to be of the order of 20 per cent when the higher crystal field parameters are added.

On the theory of pseudocontact N.M.R. shifts due to lanthanide complexes

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On the theory of pseudocontact N.M.R. shifts due to lanthanide complexes