Paramagnetic lanthanide anion

Bimetallic complexes formed using a lanthanide tris (3-diketonate and silver 3-diketonate are useful shift reagents for soft Lewis bases such as alkenes, aromatics, phosphines, and halogenated compounds.Chiral lanthanide tris (3-diketonates of tfc and hfc are used in forming the binuclear reagents. A variety of silver 3-diketonates have been evaluated, but only the silver chelate of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione [Ag (fod)] is commercially available. The mixture forms a tetrakis chelate anion to which the silver is ion paired ([Ln (P-dik)4 ]Ag" "). In the bimetallic reagent, the silver binds to the soft Lewis base while the paramagnetic lanthanide ion causes perturbations in the chemical shifts that account for the enantiomeric discrimination. 

Paramagnetic shifts may be induced in cations which associate with suitable lanthanide complexes. Thus in aqueous solution, [M(hpda)3]6, where M = Dy or Tm and H3hpda = 4-hydroxypyridine-2,6-dicarboxylic add, associates with Mg2-1, 39K+, 23Na+, 87Rb+ or 14NH4 and produces shifts of up to 25 p.p.m. which are most marked above pH 7.582 A similar effect is shown for cations (and anions and uncharged molecules) by lanthanide tetra-p-sulfonatophenyl-porphyrins in aqueous solutions.583 This is discussed in Section 39.2.6.3, as are the large shifts produced in aqueous solution by Na[Eu(dota)(H20)] (H4 dota = 23).584... 

The ions Y, La + and Lu + are diamagnetic, as are Yb and Ce also. All the other lanthanide ions are paramagnetic. Owing to the shielding of the 4f-electrons from the chemical enviromnent, complexing groups or anions bound to paramagnetic Ian-... 

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