Structural systematics in actinide fluoride complexes

Hydrothermal Syntheses, Structures, and Magnetic Properties of the U(IV) Fluorides (C5H14N2)2U2F12·5H2O and (NH4)7U6F31

“…The geometry about the U(IV) centers varies between square antiprisms, dodecahedra, and bicapped trigonal prisms. Because minor distortions are su$cient to interconvert these CN8 geometries and the observed geometries do not frequently conform to the ideal symmetry, the qualitative description of these coordination polyhedra is inexact at best (29). The bond valence sums for U(1) and U(2) are 4.07 and 4.10, respectively, which are consistent with the structure and formula assignments (32,33).…”

Organically Templated Zirconium Fluorides: Hydrothermal Syntheses, Structural Relationships, and Thermal Behavior of (C2H10N2)Zr2F10·H2O and (C4H12N2)ZrF6·H2O

“…The vastly reduced complexity of the compositional diagrams for the zirconium systems versus those of uranium is explained by both the redox character of uranium, which allows for U(IV) and U(VI), and uranium's increased size, making UF units common. Coordination numbers beyond eight are rare for zirconium #uorides (excluding cluster compounds with interstitial #uoride) (18). Redox processes are essentially absent from zirconium #uorides, which actually abridges the chemistry in a fortuitous manner and provides a high yield route to pure phases in the form of large single crystals.…”

“…Our recent studies on the hydrothermal syntheses of organically templated low-dimensional U(IV) #uorides (6,8) and aquo#uorides (9) has prompted us to explore similar chemistry with Zr(IV) as has been accomplished in hightemperature solid-state reactions between UF or ZrF and alkali metal #uorides (18). Abrahams and coworkers have recently reported improved methods for isolating singlephase materials for several zirconium #uorides with known inorganic structural features (17).…”

Alkali metal actinide complex halides : thermochemical and structural considerations

“…Although UO,I, adducts with organic molecules have been reported [I], the preparation of this compounds and its hydrates has been attempted several times without success. Brandenburg [46] suggested through a correlation method involving numerous compounds a value of -1 000 2 4 kJ . mol-' for its enthalpy of formation.…”

“…Fluoro-complexes. -A very large number of actinide fluoride complexes have been characterized, in which the actinide cation is displaying a coordination which can vary from 6 to 9, and preparative, structural and spectral studies on these compounds have adequately been reviewed [1][2][3]. Our knowledge on the enthalpies of formation of such species is so far restricted to a number of uranyl compounds [4][5][6] with the general formulae M;U0 2 F ; , M'(U0 2 ) 2 F 5 and M;(U0 2 ) 2 F 9 (M' variously Na, K, Rb and Cs).…”