Actinide oxide fluorides

The known actinide oxide fluorides are shown in Table II. 

Preparations and reactions of oxide fluorides of the transition metals, the lanthanides and the actinides. J. H. Holloway and D. Laycock, Adv. Inorg. Chem. Radiochem., 1984, 28, 73 (278). 

S.A. Kinkead, K.D. Abney and T.A. O Donnell, f-element speciation in strongly acidic media lanthanide and mid-actinide metals, oxides, fluorides and oxide fluorides in superacids 507... 

PREPARATIONS AND REACTIONS OF OXIDE FLUORIDES OF THE TRANSITION METALS, THE LANTHANIDES, AND THE ACTINIDES... 

The lanthanides, unlike the transition metals and the actinides, tend not to form compounds over a range of oxidation states. The +3 oxidation state is characteristic of all of the lanthanides, and the oxide fluorides of formula LnOF (Ln = lanthanide metal) are well known. The less stable oxidation states of + 2 and + 4 are known, but the latter is represented only by the dioxides and tetrafluorides of cerium, praseodymium, and terbium, and no tetravalent oxide fluorides have been reported. 

Other actinide(VI) oxide fluorides exist. The thermal decomposition of UOF4 at 290°C (226) and the reaction of uranyl fluoride with SeF4 (275) yield a yellow solid, which is U203F6. The compound U205F2 is formed as the dihydrate in the U03-HF-H20 system (276) and when UF6 reacts with a small quantity of water, U305F8 is the product (275). 

Preparations and Reactions of Oxide Fluorides of the Transition Metals, the Lanthanides, and the Actinides John H. Holloway and David Laycock... 

There are no experimental data for the heat capacity and therefore entropy of p-ThCk and we have accepted the estimated value of the entropy of Konings [2004KON], based on a systematic set of lattice and electronic contributions to the entropies of the oxides, fluorides and chlorides of the actinide elements, as described in Appendix A. 

The heat capacity data of the actinide(IV) oxides, fluorides and chlorides have been analysed, and the data expressed as the sum of three contributions from the lattice vibrations, from /-electron excitation and from a residual term, probably arising from the interaction of ri-electrons. It is demonstrated that the latter contribution becomes zero around T = 500 to 600 K. A similar approach is given for the entropies, from which the standard entropies of a number of An(IV) compounds have been estimated. 

The absence of reliable thermodynamic data for the tetrafluorides has contributed to difficulties in defining the chemistry of the rare earth elements. The fact that only Ce, Pr, and Tb form stable Rp4(s) phases has been established (see section 2.4) however, the thermochemistry of these fluorides has remained uncertain. Insight is provided by the work of Johansson (1978), who has correlated data for lanthanide and actinide oxides and halides and derived energy differences between the trivalent and tetravalent metal ions. The results, which have been used to estimate enthalpies of disproportionation of RF4 phases, agree with preparative observations and the stability order Prp4< TbP4 < CeP4. However, the results also indicate that tetravalent Nd and Dy have sufficient stability to occur in mixed metal systems like those described by Hoppe (1981). 

---