Lanthanide elements 4-2 oxidation state

AH of reaction (17) is an estimate since PuCl4(s) has not been synthesized AfH° [PuCl4(s)] = — 964 kJ is an estimate (Fuger et al. 1983). The dramatic difference in these enthalpies [Pu(IV) is more stable than Pu(III) in this complex chloride by -95-( —4) = - 91 kJ or almost 1.0 V, in comparison with the binary chloride] shows how acid-base effects influence oxidation-reduction properties. As noted above, there are few known lanthanide (IV) complex halides and no thermodynamic data on even these few halides, so no quantitative comparison can be made. Nevertheless it does show how complexation effects by basic complexants make high f-element oxidation states attainable. Perhaps the most dramatic evidence of the enhancement of high oxidation state by a basic fluoride is the existence of the Nd(IV) and Dy (IV) compounds such as Cs2(Cs, Rb, K) (Nd, Dy)Cl2 these AjRF, double fluorides are the only known Nd (IV) and Dy(IV) compounds. 

Reference has been made already to the existence of a set of inner transition elements, following lanthanum, in which the quantum level being filled is neither the outer quantum level nor the penultimate level, but the next inner. These elements, together with yttrium (a transition metal), were called the rare earths , since they occurred in uncommon mixtures of what were believed to be earths or oxides. With the recognition of their special structure, the elements from lanthanum to lutetium were re-named the lanthanons or lanthanides. They resemble one another very closely, so much so that their separation presented a major problem, since all their compounds are very much alike. They exhibit oxidation state -i-3 and show in this state predominantly ionic characteristics—the ions. 

Evidence other than that of ion-exchange favours the view of the new elements as an inner transition series. The magnetic properties of their ions are very similar to those of the lanthanides whatever range of oxidation states the actinides display, they always have -1-3 as one of them. Moreover, in the lanthanides, the element gado-... 

Uranium is the fourth element of the actinide (SJ series. In the actinide series the electrons are more effectively shielded by the Is and 7p electrons relative to the 4f electrons (shielded by 6s, 6p) in the lanthanide (4p series. Thus, there is a greater spatial extension of 5f orbitals for actinides than 4f orbitals for lanthanides. This results in a small energy difference between and 5/ 6d7s electronic configurations, and a wider range of oxidation states is... 

The redox behaviour of Th, Pa and U is of the kind expected for d-transition elements which is why, prior to the 1940s, these elements were commonly placed respectively in groups 4, 5 and 6 of the periodic table. Behaviour obviously like that of the lanthanides is not evident until the second half of the series. However, even the early actinides resemble the lanthanides in showing close similarities with each other and gradual variations in properties, providing comparisons are restricted to those properties which do not entail a change in oxidation state. The smooth variation with atomic number found for stability constants, for instance, is like that of the lanthanides rather than the d-transition elements, as is the smooth variation in ionic radii noted in Fig. 31.4. This last factor is responsible for the close similarity in the structures of many actinide and lanthanide compounds especially noticeable in the 4-3 oxidation state for which... 

This state is found for the six elements Am and Cf No, though in aqueous solution only for Fm, Md and No. However, for No, alone amongst all the f-series elements, it is the normal oxidation state in aqueous solution. The greater stabilization of the +2 state at the end of the actinides as compared to that at the end of the lanthanides which this implies, has been taken " to indicate a greater separation between the 5f and 6d than between the 4f and 5d orbitals at the ends of the two series. This is the reverse of the situation found at the beginnings of the series (p. 1266). 

Unsubstituted bisphthalocyanines 2 are formed in the presence of several elements which exist in a stable oxidation state of + III or +IV such as titanium, zirconium, hafnium, indium and most of the lanthanide and actinide elements. 

Unusual oxidation states of some actinide and lanthanide elements. L. B. Asprey and B. B. Cunningham, Prog. Inorg. Chem., 1960, 2, 267-302 (245). 

Recent advances in the chemistry of the less common oxidation states of the lanthanide elements. D. A. Johnson, Adv. Inorg. Chem. Radiochem., 1977, 20, 1-133 (599). 

Recent Advances in the Chemistry of the Less-Common Oxidation States of the Lanthanide Elements D. A. Johnson... 

The principle just outhned has two parts. The first part deals with redox processes and was developed here by examining the relative stabihties of the -i-2 and -i-3 oxidation states of the lanthanides. It can be extended in a variety of ways. Thus if the f variation is shifted one element to the right, it tells us the nature of the f variations, and accounts for the distribution of the -i-4 oxidation states of the lanthanides [2, 10, 15]. Their stability shows maxima at cerium(IV) and terbium(IV), decreasing rapidly as one moves from these elements across the series. 

One of the distinctive aspects of transition-metal and lanthanide chemistry is cluster formation via metal-metal bonding that is characteristic of many of these elements in low oxidation states [1]. The unique structural, chemical, and... 

A predominant feature of the atomic structure of the lanthanide group is the sequential addition of 14 electrons to the 4f subshell (Table 1). The /"electrons do not participate in bond formation and in ordinary aqueous solutions all of the lanthanides exhibit a principal (III) state. The common (III) state confers a similarity in chemical properties to all lanthanide elements. Some of the lanthanides can also exist in the (II) state (Nd, Sm, Eu, Tm, Yh) or in the (IV) state (Ce, Pr, Nd, Tb, Dy). Except for Ce(IV), Eu(II), and Yb(II), these unusual lanthanide oxidation states can only be prepared under drastic redox pressure and temperature conditions, and they are not stable in aqueous solutions. Cerium (IV) is a strong oxidizing agent... 

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