Nitrates ionic radii

Most lanthanide compounds are sparingly soluble. Among those that are analytically important are the hydroxides, oxides, fluorides, oxalates, phosphates, complex cyanides, 8-hydroxyquinolates, and cup-ferrates. The solubility of the lanthanide hydroxides, their solubility products, and the pH at which they precipitate, are given in Table 2. As the atomic number increases (and ionic radius decreases), the lanthanide hydroxides become progressively less soluble and precipitate from more acidic solutions. The most common water-soluble salts are the lanthanide chlorides, nitrates, acetates, and sulfates. The solubilities of some of the chlorides and sulfates are also given in Table 2. 

The increase in i>p 0 is due to a progressive increase in the coupling of M-0 and P-0 vibrations with an increasing atomic number of the lanthanide ion. Similarly, McRae and Karraker (201) have found that the Pp 0 increases with decreasing ionic radius in the complexes of TPP with lanthanide nitrates. This trend has, however, been explained by them in terms of relative influence of attractive and repulsive forces in these complexes. As the size of the lanthanide ion decreases, the repulsive forces in-... 

A preferential uptake of the Ba " ion (due to having an ionic radius close to that of the ammonium ion) among the alkaline earth metals also confirms this hypothesis. At the same time, the affinity for other divalent elements is at least one order of magnitude higher than that for alkali or alkaline earth metal cations. The Kd values for most transition metals and lead are in the range from 20000 to more than 100000. However, the absolute values of their uptake in 0.1 M metal nitrate solutions are relatively low. The lEC values are higher than 1.0 meq g" for only two ions, Cu and Hg. ... 

In addition to the ionic radius in the hydrated state, the valency of an ion is another solute-specific property that affects retention. In general, retention is shifted forward with increasing valency. Thus, the monovalent nitrate elutes prior to the divalent sulfate. Exceptions are multivalent ions such as orthophosphate, where the retention depends on the eluent pH due to different dissociation equilibria. However, the size of an ion often influences the retention more strongly than the valency. Hence, the divalent sulfate elutes prior to the monovalent, but strongly polarizable, thiocyanate. 

Figure 7. Log D vs. ionic radius for typical divalent cations in the HDEHP-aqueous nitrate system (21)...

Figure D-5 Empirical relations between interaction coefficients of simple cations, charge z and ionic radius r in nitrate media.

Ethanol has also received considerable attention as a solvent over a long period of time. Data on this solvent, however, are rather few compared to methanol and very few systematic studies exist. Several solubility studies have been made since the publication of Seidell and Linke. Thomas has reported solubilities for the alkali metal iodides at 20 and 25°C, and observed a decrease in solubility with an increase in ionic radius of the cation. Deno and Berkheimer have reported the solubilities of several tetraalkylammonium perchlorates. In every case the solid phase was the pure salt. Solubilities for several rare earth compounds have been reported.Since all of these salts form solvates in the solid phase, the results cannot be used in thermodynamic calculations without the corresponding thermodynamic values for the solid phases. Solubilities of silver chloride, caesium chloride, silver benzoate, silver salicylate and caesium nitrate have been measured in ethanol, using radioactive tracer techniques. Burgaud has measured the solubility of LiCl from 10.2 to 57.6°C and observed that there is a transition from the four-solvated solid phase to the non-solvated phase at 20.4°C. 

The formation of inactive complexes is accompanied by a complexation of a nitrate anion and a large Au(in) cation, 2 ,2 or 2 The formation of these charged species should be more favourable in a polar solvmt such as CH3CN. This explains why self-inhibition is more pronounced in CH3CN than in CF3CH2OH (for additional discussion see section 15). Au(in)-Br complexes are larger than similar Au(III)-Cl complexes because the ionic radius of Br in crystals is higher than that of Cr, 1.96A and 1.81, respectively. The enthalpy of... 

FIGURE 2.11 Ionic radius and ion-pair dissociation for Cs, Rb, K, Na nitrates in... 

What is the reason for these similarities Primarily it is a size effect. The Hthium and magnesium ions (ionic radii = 0.73 A and 0.86 A, respectively) are of appropriate size to fit into a lattice formed by oxide ions (ionic radius = 1.26 A) such that the attraction of cations and anions is maximized and the repulsions between the larger anions is minimized. (See Chapter 8 for more details on solid-state energetics.) The carbonate and nitrate anions (radii = 1.78 A and 1.79 A, respectively) are just large enough that they get in one another s way, and their mutual repulsions become more of a dominant factor. Accordingly, the carbonates and nitrates decompose to the more energeticaUy favorable oxides. 

Preston (1985) described the solvent extraction behavior of a large number of metal cations including rare earth nitrates in solutions of Versatic 10 (2-ethyl-2-methylheptanoic acid), naphthenic, 2-bromodecanoic and 3,5-diisopropylsalicylic acids in xylene. The last two acids extract metal cations under more acidic conditions, pH 1-2. For Versatic 10 the order of extraction of yttrium and lanthanides is La < Ce < Nd < Gd < Y < Ho < Yb and for naphthenic acids it is La < Ce < Y < Nd < Gd k Ho Yb. The lanthanides tend to form complexes of predominantly ionic nature. In the case of Versatic 10, the stability of the complexes increases uniformly with atomic number due to the increase in electrostatic energy as a result of the decrease in ionic radius. The primary branched naphthenic acid allows the formation of complexes with high coordination number, nine for La to Nd, eight and eventually six as the metal ionic radius decreases. In general, the extraction of a metal ion by a carboxylic acid H2A2 can be represented by the reaction... 

The unit cell values show a rather linear decrease with the increasing M ionic radius, with Y between Dy and Ho. Both the diselenite and nitrate anions coordinate to the trivalent M ions as shown by the IR data on the Y compound, Niinisto et al. [1]. 

---