Tripositive ions

The valences of the rare-earth metals are calculated from their magnetic properties, as reported by Klemm and Bommer.14 It is from the fine work of these investigators that the lattice constants of the rare-earth metals have in the main been taken. The metals lutecium and ytterbium have only a very small paramagnetism, indicating a completed 4/ subshell and hence the valences 3 and 2, respectively (with not over 3% of trivalent ytterbium present in the metal). The observed paramagnetism of cerium at room temperature corresponds to about 20% Ce4+ and 80% Ce3+, that of praseodymium and that of neodymium to about 10% of the quadripositive ion in each case, and that of samarium to about 20% of the bipositive ion in equilibrium with the tripositive ion. 

Moeller, T. and Hseu, T. M. (1962). Observations on the rare earths— LXXVI. The stabilities of the trans-1,2, diaminocyclohexane-N,N tetraa-cetic acid chelates of the tripositive ions, J. Inorg. Nucl. Chem. 24, 1635. 

Np through Lr are all prepared artificially by bombardment with neutrons and/or light element ions (He-4, B-10, B-11, C-12,0-16,0-18, Ca-48, Fe-56). Some routes are presented in Table 18.1. The elements have been separated from the targets and other product species by redox reactions, ion exchange, and solvent extraction. In a typical separation, a sulfonic acid ion exchange resin is placed in a column, the tripositive ions of Am through Lr are poured into the column where they are taken up, then the column is eluted with a solution of ammonium a-hydroxybutyrate. As elution proceeds, the An+ ions come off in this order Lr-Md-Fm-Es-Cf-Bk-Cm-Am. They are detected by the distinctive energies of their radioactive emissions. 

Alternative values for heats of formation of some hydrated tripositive ions have been obtained197 from a reanalysis of the first half-wave amalgamation potentials, ( 1/2)1. These values, together with standard reduction potentials,198 are given in Table 3. 

Figure 9 Energy levels of some representative lanthanide tripositive ions. Ce and Pr, full set Eu and Tb, partial set (energy values taken from S. Hiifner, Optical Spectra of Transparent Rare Earth Compounds , Academic Press, 1978)...

Not all the lanthanide ions give rise to f-f transitions, including obviously the f and f species, La + and Lu +. Likewise there are no f-f transitions for the f (Ce +) and f(Yb +) ions, as with only a single L-value there is no upper 4f state. Transitions between Fs/2 and Fv/2 are seen in the case of Ce + as a rather broad band in the infrared region around 2000 cm Ce + and Yb +do, however, give rise to broad 4f" 4f" 5d transitions (as indeed do many lanthanides). Even an ion like Eu +, which has several absorptions in the visible region of the spectrum, has only weak absorptions, so many of its compounds appear colourless the only three tripositive ions whose compounds are invariably coloured are Pr +, Nd +, and Er +. 

The monosulfides of the rare earth elements behave differently from that discussed here since these are metal-like for all but those elements forming the most stable divalent states. Here a general proclivity towards forming tripositive ions seems more important (as in the metals themselves)—a property usually considered to result from a fortuitous balance between ionization and lattice or solvation energies. The sulfides have also been interpreted in terms of a degeneracy of the upper 4f levels with a 5d band (where applicable) (10). In contrast to the halides, there is little differentiation of the electrical properties among the monosulfides, monoselenides, and monotellurides (29). 

Although several factors appear to mitigate against their formation, many complex species derived from the lanthanide ions have been described (36). Some of these appear to exist only as ion pairs in solution and do not have sufficient stability to permit them to carry through series of reactions without concomitant dissociation. Others exist only in the solid state and dissociate or decompose upon dissolution. Still others are of sufficient stability to exist as such, both in solution and as isolable solids. Essentially all of the species described are derived from the tripositive ions, and essentially no information is available relative to complex species in nonaqueous systems. A broad classification of typical species is given in Table I (36). 

Scandium is still a neglected element. It is the most expensive metal in its period (caused by the fact that its even distribution in the earth means that there are no rich ores) and its chemistry is virtually exclusively that of the +3 oxidation state, so that it is not classed as a transition metal and is often silent to spectroscopy and not amenable to study by many of the usual spectroscopic tools of the coordination chemist. Chemists have often either tended to assume that complexes of Sc are just like those of the tripositive ions of the transition metals or that they resemble lanthanide complexes. Neither of these assumptions is correct—how incorrect we are now realizing. Scandium chemistry is starting to exhibit characteristics all of its own, and possibly the burgeoning use of scandium compounds in organic synthesis may drive a real expansion of scandium chemistry. 

In conclusion, we have demonstrated how it is possible to build up quite a detailed picture of the microstructure of the ionic phase of neutralized Nafion membranes by exploiting the magnetic properties of iron ions, and obtaining Mossbauer spectra at low temperatures in an external magnetic field. Results common to the two Mossbauer cations (Fe2+ and Fe +) concerning the anomalous character of the aqueous phase can reasonably be expected to apply for any other cation. The tendency or Fe3+ ions to form pairs and larger groups is not shared by Fe2, and it may be a special feature of small tripositive ions. 

Aluminum that has a protective coating of aluminum oxide is less reactive than elemental aluminum. Aluminum forms only tripositive ions. It reacts with hydrochloric acid as follows ... 

The other Group 3A metallic elements form both unipositive and tripositive ions. Moving down the group, we find that the unipositive ion becomes more stable than the... 

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