Paramagnetic lanthanides

NMR investigation of molecular structure of paramagnetic lanthanide complexes with crown ethers in solutions 98ZSK714. 

Paramagnetic lanthanide shift reagents in n.m.r. spectroscopy principles methodology and applications. J. Reuben, Prog. Nucl. Magn. Reson. Spectrosc., 1973, 9, 3-70 (280). 

NMR spectroscopy the NMR spectrum of the sample in the presence of a chiral solvating agent (see Section 3.1.4.1.) or a chiral paramagnetic lanthanide shift reagent (see Section 3.1.4.2.2.) is recorded. The determination of enantiomeric purity rests on the nonequivalence of externally enantiotopic nuclei which are rendered externally diastereotopic in a non-racemic chiral environment. 

Chemical shift differences dj, s<5 are usually small. They can be enhanced by the addition of an achiral paramagnetic lanthanide shift reagent84. Thus, Eu(fod)3 (see Section 3.1.4.2.) altered the magnitude, and occasionally the sense of spectral nonequivalence, of racemic sulfoxides in the presence of nonracemic perfluoroalkylcarbinols85. 

Ln refers to paramagnetic lanthanide cations other than Gd. 

NMR Spectra of Paramagnetic Lanthanide Complexes 39,2.9,1 Introductory summary... 

As a matter of historical introduction it is noted that the first application (4) of a paramagnetic lanthanide chemical shift reagent involved the simplification of the proton NMR spectrum of cholesterol by means of Eu(dpm)3-2py. The applications and development of these valuable reagents are the subject of a book (5) and a recent review. (6)... 

In a study combining 2H relaxation-time measurements and use of paramagnetic lanthanide shift reagents, the ratio of the relaxation times of axial and equatorial deuterons in 2,2,6,6-tetradeuterio-4-t-butylcyclohexanone [20]... 

The paramagnetic properties of the lanthanides have been exploited in NMR spectroscopy for many years [16,17], The paramagnetic lanthanide induced shift is generally considered as the sum of the contact and pseudocontact terms (Equation 1) [16-18]... 

Contact shifts and through-bond spin de-localisation in paramagnetic lanthanide cally rigid ligands 3.1. Complexes with threefold symmetry ... 

Separation of contact and pseudo-contact contributions in paramagnetic lanthanide complexes 372 (L4 = tris 2-[A -methylcarbamoyl-(6-W,A -diethylcarbamoyl)pyridi-ne-2)ethyl]amine ) 390... 

Nuclear relaxation in paramagnetic lanthanide complexes for extracting R-nucleus distances... 

For any nucleus i of a paramagnetic lanthanide complex in the absence of significant chemical exchange, the experimental longitudinal (l/7 p) and transversal (1 /7 xp) nuclear relaxation rates are given by eqs. (4), (5) in which 7]dia corresponds to the characteristic relaxation times of the same nucleus i in the analogous diamagnetic complex (R = La, Y, Lu) and 7)para are... 

This equation justifies the qualitative statement that the shorter the electronic relaxation times, the smaller paramagnetic effects on nuclear relaxation. It also predicts that the dipolar contribution is maximum for strongly paramagnetic lanthanides (via /ueff) and for nuclei located close to the metal ion (via r ). 

Contact shifts and through-bond spin delocalisation in paramagnetic lanthanide complexes... 

Separation of contact and pseudo-contact contributions in paramagnetic lanthanide... 

J. Reuben and G.A. Elgavish, Shift reagents and NMR of paramagnetic lanthanide complexes 483... 

J.H. Forsberg, NMR studies of paramagnetic lanthanide complexes and shift reagents 1... 

Addition of a small amount of a paramagnetic lanthanide shift reagent to a solution of ligand results in chemical shift of the ligand NMR spectrum which is proportional to Ln/L ratio at low values. The condition of rapid chemical exchange must prevail when tb, the mean lifetime of the complex is much shorter than 1 /Ab. The condition is Tb [Pg.796]

Paramagnetic lanthanides induce chemical shifts in the NMR spectrum of the ligands in their vicinity. The origin of the shift is the dipolar interaction of the nuclear magnetic... 

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