Trivalent temperature dependence

The [Fe(phen)3]3+ complex dissolved in water is known to behave as a hydrophobic ion, as demonstrated by the ion association with o- and m-benzenedisulfonate and 2,6- and 2,7-naphthalenedisulfonate ions, which was investigated by the conductivity method. Similar hydrophobic properties were also observed for trivalent [Co(phen)3]3+ and [Co(bpy)3]3+ complexes.2 In the present study, the temperature dependence of molar conductivities of [Fe(phen)3]2+, [Co(phen)3]3+, and [Co(bpy)3]3+ as well as the ion association with chloride and perchlorate ions were examined in order to elucidate the effect of the ionic charge on the hydrophobic interactions. 

A weak temperature dependence is encountered in those cases where the excited state shows only a very small amount of relaxation. Energy migration persists down to low temperatures. In this category we find compounds of Mn, U and the trivalent rare earth ions. 

Fig. 12. Upper part First experimental evidence from Mossbauer effect data on SmBg of the existence of a mixed configuration ground state of Sm (Ref. 33). The Sm isomer shift is found to be intermediate between values of divalent (Sm2+) and trivalent (Sm3+) compounds furthermore it is temperature independent. Lower part Temperature dependence of the susceptibility, from Ref. 34. Most significant result is the absence of a divergence of x at low temperatures. The small rise below 10 °K does not show 1/T dependence and was attributed to impurity effects.

A considerable number of lanthanides show valence instabilities. Among them Sm, Eu, Tm and Yb are able to fluctuate between the trivalent and divalent electronic configurations, depending on the environmental conditions. On the tetravalent side, although Pr and Tb are suspected to have some hybridization of localized-conduction states, only Ce clearly shows such an effect. Some of its compounds are unique for the study of the electronic fluctuation between the trivalent and tetravalent configurations. The 4f electron hybridization is the origin of the Ce demagnetization, volume reduction, anomalous temperature dependence of the transport properties, and a number of other abnormal behaviours. 

Titanium, e.g., cannot have a higher valency than four and it has that valency in Ti02- However, some of its atoms can have a lower valency if some oxygen is lost from the lattice. This results in some loss of energy but there is an increase in entropy. The stoichiometry then determines the temperature-dependent conductivity. Cobalt oxide (CoO), on the other hand, tends to be p-type semiconducting because it is easier to form trivalent cobalt by some uptake of oxygen... 

The recent measurements of the temperature dependence of the electrical restivity of (LaSm)Sni alloys by Bakanowski et al. (1977) indicate the presence of resistivity minima in the samples studied (all of which were for Sm concentrations of less than 20 at.%). These observations wo.uld favor a more nearly trivalent state for Sm in LaSns and clearly support the presence of a Kondo effect in (LaSm)Sn3 alloys. However, the situation is incomplete at the time of this writing further data may reveal an entirely new class of behavior represented by this interesting system. 

It is expected that liquid Sc, Y, La, and Lu should have similar magnetic properties. All should be trivalent, exhibit no 4f character, and show some effect of the d-level at the Fermi energy. [Some differences in Xa l e been noted for these metals, at least at low temperatures T < 300 K). In particular, while Xa Y and Lu are similar, and weakly temperature-dependent, Xa Sc shows some Curie-Weiss behavior. (See McEwen 1978.)] Xa for liquid La has been measured. It is temperature independent, and is characteristic of Pauli paramagnetism. 

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