Cations lanthanides

Poly(ether ketone) dendrons [24] have been observed to show an antenna effect toward lanthanide cations, especially for Eu +. Two focal coordination forms were examined, namely carboxylate [25] and 1,3-diketonate [26]. The use... 

Although the lanthanide cations most commonly give complexes with coordination numbers of 8 or 9, the [ML3(LH)3] species predominate on extraction with phosphorus(V) acids and it has been suggested that the bulk of the L- LH chelate ring favors a lower coordination number 4 The phosphorus(V) acids are very effective reagents for the extraction and separation of lanthanides.124 (See chapter 3.2). 

Figure 2.6 Types of orientations between the electronic pair of a ligand and a lanthanide cation, (a) The lone pair is directly oriented towards the lanthanide cation.

The greater ease of forming lanthanide cations compared to forming transition metal... 

Trivalent lanthanide cations have luminescent properties which are used in a number of applications. The luminescence of the lanthanide ions is unique in that it is long-lasting (up to more than a millisecond) and consists of very sharp bands. Lanthanide emission, in contrast to other long-lived emission processes, is not particularly sensitive to quenching by oxygen because the 4f electrons found within the inner electron core... 

The complexing ligand of the lanthanide cation also provides a way for the luminescent lanthanide complex to be linked to a particular target molecule, thus acting as a luminescent probe for the target... 

Another area where titration calorimetry has found intensive application, and where the importance of heat flow versus isoperibol calorimetry has been growing, is the energetics of metal-ligand complexation. Morss, Nash, and Ensor [225], for example, used potenciometric titrations and heat flow isothermal titration calorimetry to study the complexation of UO "1" and trivalent lanthanide cations by tetrahydrofuran-2,3,4,5-tetracarboxylic acid (THFTCA), in aqueous solution. Their general goal was to investigate the potential application of THFTCA for actinide and lanthanide separation, and nuclear fuels processing. The obtained results (table 11.1) indicated that the 1 1 complexes formed in the reaction (M = La, Nd, Eu, Dy, andTm)... 

Vanadates For the isostructural strontium and barium ortho-vanadates the V-—0 vibrational frequencies decrease with increasing effective nuclear charge [51]. Similar orthovanadates with the apatite structure have for a given halogen ion decreasing frequencies of the VO4 ion in the order Ca>Sr >Ba ((62) and Table 4]. However, it is impossible to see any trend towards the tiivalent lanthanide cations (59). The IR bands are so wide in this case that small changes cannot be measured. 

To date, D coefficients of carbohydrates established with the PFGSE approactf - " have been undertaken to (1) validate the theoretical self-diffusion coefficients calculated from MD trajectories, (2) demonstrate the complexation of lanthanide cations by sugars,(3) probe the geometry of a molecular capsule formed by electrostatic interactions between oppositely charged P-cyclodextrins, (4) study the influence of concentration and temperature dependence on the hydrodynamic properties of disaccharides, and (5) discriminate between extended and folded conformations of nucleotide-sugars. ... 

Ln refers to paramagnetic lanthanide cations other than Gd. 

It is inappropriate here to discuss details of nmr spectroscopy. However, the full possibilities for structural studies arise from the use of probes that bind to the molecule under study and perturb the nmr spectrum. These probes are generally paramagnetic species, in particular the lanthanide cations. In the nmr spectrum separate signals arise from each nucleus in the molecule, provided that the nucleus possesses a nonzero nuclear spin (e.g., H, 13C, 14N). The extent of the spectral perturbations of a given signal depends on the relative geometries of the paramagnetic species and the nucleus in question. Thus structural parameters can be obtained, in principle, for most atoms (nuclei) in a protein molecule.5... 

Fig. 1. Representation of the active site region of hen lysozyme, from the X-ray structure (adapted from Ref. 31). The lanthanide cations bind in the region between asp 52 and glu 35.

Solutions of dipositive lanthanide cations have been obtained in liquid ammonia, ethanol, THF, acetonitrile and hexamethylphosphoramide. Ions stabilized, or for which there is evidence for stabilization, include Nd2+, Dy2+ and Tm2+ as well as Eu2+, Yb2+ and Sm2+. The non-hydroxylic solvents are best at stabilizing M2+ ions. Thus NdCl2(THF)2 has been reported from the reduction of NdCl3 in THF by Na(naphthalene),657 and corresponding reductions of MC13 (M = Eu, Yb or Sm) have also been achieved.658 Solutions of solvated MI2 (M = Sm or Yb) in THF may easily be made by the quantitative reaction of the metal with 1,2-diiodoethane, producing ethane. The solid THF adducts may be isolated.659... 

In Figure 26-3, an [H+l gradient was used for a cation-exchange separation. The column for this separation has nitrilotriacetic acid groups that bind lanthanide cations in the order... 

The absorption spectra of the lanthanide +3 cations are shown in Fig. 14.7. These spectra result from f-f transitions analogous to the d-d transitions of the transition metals. In contrast to the latter, however, the broadening effect of ligand vibrations is minimized because the 4/orbitals in the lanthanides are buned deep within the atom. Absorption spectra of the lanthanide cations are thus typically steip and line-like as opposed to the broad absorptions of the transition metals. 

The simplest recognition process is that of spherical substrates these are either positively charged metal cations (alkali, alkaline-earth and lanthanide cations) or the negative halide anions (see Chapt. 3). 

---