Lanthanide ion

It has been usual to assume that the lanthanide ions undergo complex-ing by the Eigen mechanism (p. 250). Step k2 is a composite process involving loss of water from the coordination shell of the lanthanide ion 

Rate data for lanthanide complexes have been summarized by Silber et al. [166]. In Fig. 9 values for nitrate and sulphate complexes are given 

Diebler, M. Eigen, G. Ilgenfritz, G. Maass and R. Winkler, Pure Appl. Chem., 20 (1969) 93. 

Kustin and J. Swinehart, in J. O. Edwards (Ed.), Inorganic Reaction Mechanisms, Progress in Inorganic Chemistry Series, Vol. 13, Interscience, 1970, p. 107. 

Langford and V. S. Sastri, in M. L. Tobe (Ed.), Reaction Mechanisms in Inorganic Chemistry, Inorganic Chemistry, Series One, MTP Review of Chemistry, Vol. 9, Butterworths, London and University Park Press, Baltimore, 1972, p. 203. 

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The reason why lanthanides of high atomic number emerge first is that the stability of a lanthanide ion-citrate ion complex increases with the atomic number. Since these complexes are formed by ions, this must mean that the ion-ligand attraction also increases with atomic number, i.e. that the ionic radius decreases (inverse square law). It is a characteristic of the lanthanides that the ionic radius... 

First, the use of water limits the choice of Lewis-acid catalysts. The most active Lewis acids such as BFj, TiQ4 and AlClj react violently with water and cannot be used However, bivalent transition metal ions and trivalent lanthanide ions have proven to be active catalysts in aqueous solution for other organic reactions and are anticipated to be good candidates for the catalysis of aqueous Diels-Alder reactions. 

Fig. 11) form very strong and selective complexes with Fe or actinide and lanthanide ions (63,64) while a similar receptor with hard endocarboxyhc acid groups is efficient for hard and ions showing again responsibility of a charge density effect in the receptor—substrate recognition (65). Thus,... 

Fig. 3. The elution of tnpositive actinide and lanthanide ions. Dowex-50 ion-exchange resin was used with ammonium a-hydroxyisobutyrate as the eluant.

Solid Compounds. The tripositive actinide ions resemble tripositive lanthanide ions in their precipitation reactions (13,14,17,20,22). Tetrapositive actinide ions are similar in this respect to Ce . Thus the duorides and oxalates are insoluble in acid solution, and the nitrates, sulfates, perchlorates, and sulfides are all soluble. The tetrapositive actinide ions form insoluble iodates and various substituted arsenates even in rather strongly acid solution. The MO2 actinide ions can be precipitated as the potassium salt from strong carbonate solutions. In solutions containing a high concentration of sodium and acetate ions, the actinide ions form the insoluble crystalline salt NaM02(02CCH2)3. The hydroxides of all four ionic types are insoluble ... 

Absorption and Fluorescence Spectra. The absorption spectra of actinide and lanthanide ions in aqueous solution and in crystalline form contain narrow bands in the visible, near-ultraviolet, and near-infrared regions of the spectmm (13,14,17,24). Much evidence indicates that these bands arise from electronic transitions within the and bf shells in which the Af and hf configurations are preserved in the upper and lower states for a particular ion. 

In general, the absorption bands of the actinide ions are some ten times more intense than those of the lanthanide ions. Fluorescence, for example, is observed in the trichlorides of uranium, neptunium, americium, and curium, diluted with lanthanum chloride (15). 

Absorption Spectra, of Aqueous Ions. The absorption spectra of Pu(III) [22541-70 ] Pu(IV) [22541 4-2] Pu(V) [22541-69-1] and Pu(VI) [22541-41-9] in mineral acids, ie, HCIO and HNO, have been measured (78—81). The Pu(VII) [39611-88-61] spectmm, which can be measured only in strong alkaU hydroxide solution, also has been reported (82). As for rare-earth ion spectra, the spectra of plutonium ions exhibit sharp lines, but have larger extinction coefficients than those of most lanthanide ions (see Lanthanides). The visible spectra in dilute acid solution are shown in Figure 4 and the spectmm of Pu(VII) in base is shown in Figure 5. The spectra of ions of plutonium have been interpreted in relation to all of the ions of the bf elements (83). 

Fluorescence and Glass Lasers. Some ions absorb light of a certain frequency emitting light of lower frequency. This is known as fluorescence. Examples of ions that fluoresce in glass are Mn(TV), Pb(II), and the lanthanide ions. 

The tetravalent ceric ion [16065-90-0] Ce , is the only nontrivalent lanthanide ion, apart from stable in aqueous solution. As a result of the... 

Cerous salts in general are colorless because Ce " has no absorption bands in the visible. Trivalent cerium, however, is one of the few lanthanide ions in which parity-allowed transitions between 4f and Sd configurations can take place and as a result Ce(III) compounds absorb in the ultraviolet region just outside the visible. 

The role of cerium in these lighting phosphors is not as the emitting atom but rather as the sensitizer. The initial step in the lighting process is the efficient absorption of the 254 nm emission Ce ", with broad absorption bands in the uv, is very suitable. This absorbed energy is then transferred to the sublattice within the crystalline phosphor eventually the activator ion is fed and emission results. Cerium, as a sensitizer ion, is compatible in crystal lattices with other lanthanide ions, such as Eu and Tb, the usual activator atoms. 

Lanthanide ions as n.m.r. chemical shift probes in biological systems. J. A. Glasel, Prog. Inorg. Chem., 1973,18, 383-413 (44). 

Complexes of lanthanide ions with N-donor ligands. J. H. Forsberg, Coord. Chem. Rev., 1973,10, 195-226 (129). 

Lanthanide ions as structural probes in biological and model systems. E. Nieboer, Struct. Bonding... 

Ionic interactions have been used to prepare lanthanide-core dendrimers. This has been achieved using a convergent synthesis, in which polyether den-drons with a carboxylic acid group at the focal point were assembled around a lanathanide cation. This involved a metathetical reaction with compounds such as Er(OAc)3, Tb(OAc)3 or Eu(OAc)3 to introduce the appropriate lanthanide ion. 

Nieboer E (1975) The Lanthanide Ions as Structural Probes in Biological and Model Systems. 

Williams RJP (1982) The Chemistry of Lanthanide Ions in Solution and in Biological Systems. 50 79-119... 

Fig. 1.1 (a) The ionization enthalpies of dipositive lanthanide ions with configurations of the type [Xe]4f" (upper plot left-hand axis), (b) The standard Gibbs energy change of reaction 1 (lower plot right-hand axis estimated value ... 

The second class of reaction is that of processes in which the 4f electrons are conserved. The obvious examples are the complexing reactions of tripositive lanthanide ions. Here the irregularities due to changes in inter-electronic repulsion almost entirely disappear. We then get the slight smooth energy change whose consequences were so familiar to 19 century chemists, who struggled vdth the separation problem. 

Fig. 1.2 Standard enthalpy changes of (a) the complexing of lanthanide ions in aqueous solution by EDTA" ( left-hand axis) (b) the standard enthalpy change of reaction 2, the dichloride being a di-f...

Calls for an explanation were answered by Jorgensen and elaborated by Nugent [26]. When a lanthanide ion moves from the aqueous to the organic phase, the nephelauxetic effect leads to a small decrease in inter-electronic repulsion within the 4f shell. This decrease varies irregularly with atomic number and is responsible for the irregularities in Fig. 1.3. 

Fig. 1.3 (a) Observed values of log where is the distribution constant for lanthanide ions between aqueous 11.4 M LiBr in 0.5 M HBr and 0.6 M (CICH2)PO OC8Hi7)2 in benzene (Ref [26a] upper plot), (b) A similar variation constructed by using the theory of Table 1.2 (lower plot see text). 

Very often, the tetrad effect is not clearly discernible in the energies of processes in which 4f electrons are conserved. It may, for example, be obscured by irregularities caused by structural variations in either reactants or products. This is especially likely given the willingness of lanthanide ions to adopt a variety of coordination geometries. There is, however, no doubt that tetrad-like patterns are often observed. But does Table 1.2 provide a convincing explanation of what is seen ... 

Lanthanide nitridoborates can be divided into three classes salt-like compounds, semiconductors, and conductors or superconductors, as already shown in Fig. 8.7. Salt-like structures are usually transparent materials, marked by the typical color of the lanthanide ion. Here we discuss only nitridoborate compounds of lanthanum. The compounds La3(B3N, ) [27], La5(B3N, )(BN3) [28], Lag(B3N6)(BN3)N [29], and La3(BN3)N all count as salt-like materials, with La, ... 

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