Cerium compounds/complexes

Th(PhCOCHCOPh)4 has been reported as being isomorphous with the corresponding protactinium(IV), uraniumflV) and cerium(IV) complexes the coordination geometry in the last is a triangular faced dodecahedron, but a more recent publication73 reports the coordination geometry of the uranium(IV) compound as square antiprismatic. 

The only complexes of lanthanum or cerium to be described are [La(terpy)3][C104]3 175) and Ce(terpy)Cl3 H20 411). The lanthanum compound is a 1 3 electrolyte in MeCN or MeN02, and is almost certainly a nine-coordinate mononuclear species the structure of the cerium compound is not known with any certainty. A number of workers have reported hydrated 1 1 complexes of terpy with praseodymium chloride 376,411,438), and the complex PrCl3(terpy)-8H20 has been structurally characterized 376). The metal is in nine-coordinate monocapped square-antiprismatic [Pr(terpy)Cl(H20)5] cations (Fig. 24). Complexes with a 1 1 stoichiometry have also been described for neodymium 33, 409, 411, 413, 417), samarium 33, 411, 412), europium 33, 316, 411, 414, 417), gadolinium 33, 411), terbium 316, 410, 414), dysprosium 33, 410, 412), holmium 33, 410), erbium 33, 410, 417), thulium 410, 412), and ytterbium 410). The 1 2 stoichiometry has only been observed with the later lanthanides, europium 33, 411, 414), gadolinium, dysprosium, and erbium 33). 

Many of the fluoride complexes are anhydrous, being prepared from melts, and even hydrates are not numerous among those prepared from aqueous solution. In the case of hydrates, the refractivity of water must be allowed for. An example of a hydrate, (NH4)3CeF7 H2O obtained in the NH4F-CeF4-H20 system (81, 86), is shown in Fig. 12. When the refractivity of H2O is subtracted, the point for the yet unknown anhydrous (NH4)sCeF7 compound falls on the line established by the known anhydrous ammonium fluoride-cerium tetrafluoride complexes. 

Solid solutions can be found also for the cerium compounds, and Rossat-Mignod et al. (1985) have discussed the system CeSbi Te. A small amount off Te doping has a pronounced effect on the magnetism of CeSb. By 4% doping the complex ordering found in CeSb gives way to simple type I order and at higher concentra-... 

The assignment of oxidation states in cerium compounds is not always an easy task. A well-known case is that of cerocene, bis(cyclooctatetraene)cerium, Ce() -C8H8)2. This complex was originally formulated as a cerium(IV) compound with two (j -CsHs) " anions (Greco et al., 1976). Later calculations indicated that the stoichiometry of cerocene is better described as [Ce + ()] -C8H8)2 ] (Neumann and Fulde, 1989). Ab initio calculations showed that cerocene is in fact a mixed valent compound, with a ground state consisting of 83%... 

Several cerium(IV) complexes of various bidentate and tetradentate hydroxypyrodinonate (HOPO) complexes have been studied as model compounds for plutonium(IV) complexes (Xu et al., 2000). Bidentate HOPO monoanions are isolelectronic with catecholate dianions and they display a similar complex formation behavior towards cerium(IV) ions. However, HOPO ligands are more acidic and form stable complexes with cerium(IV) at lower pH values than catechol. The tetradentate ligands form more stable complexes than the corresponding bidentate ligands. New types of chelators for cerium(IV) and pluto-nium(IV) are the 2,3-dihydroxyterephthalamides (Gramer and Raymond, 2004 Xu et al., 2004). Some authors have made comparisons between the coordination chemistry and the redox behavior of cerium and berkelium (Lebedev et al., 1975 Milyukova et al., 1980 Yakovlev et al., 1982). 

In a recent paper, Moutarlier et al. [15] have claimed that the use of cerium salts in sol-gel-based corrosion protection is limited due to the high solubility of the cerium ions. In all of the papers cited here, the authors limited themselves to the use of cerium chloride or cerium nitrate. In order to examine the influence of alternative anions, in the present study, cerium sulphate, cerium acetate hydrate (cerium Ac) and cerium acetylacetonate (cerium Acac) have been compared to cerium nitrate and cerium chloride. Additionally, attempts were made to limit the solubility of cerium chloride and cerium nitrate with the addition of acetylacetone to form complexes of the cerium ions. Table 10.1 gives the solubilities of the cerium compounds examined in this study. 

The greater lability of 1-benzothiepin 1-oxides, compared to the parent compounds, may lead to differences in chemical behavior. Thus, treatment of the tricarbonyliron complex of 1-benzo-thiepin 1-oxide (8, X = SO) with ammonium cerium(IV) nitrate in acetone at — 30 °C leads, with the loss of sulfur monoxide, to naphthalene. In contrast, the iron ligand can be removed selectively from the corresponding 1-benzothiepin by ammonium cerium(IV) nitrate.23 92 For the synthesis of 1-benzothiepin 1-oxide, see Section 2.1.4.1,... 

Ceric ions react rapidly with 1,2-diols. There is evidence for chelation of cerium and these complexes are likely intermediates in radical generation10 106 The overall chemistry may be understood in terms of an intermediate alkoxy radical which undergoes p-scission to give a carbonyl compound and a hydroxyalkyl radical (Scheme 3.59). However, it is also possible that there is concerted electron transfer and bond-cleavage. There is little direct data on the chemical nature of the radical in termediates. 

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