Synthèse et caractérisation des oxypentafluorouranates(VI) NH₄UOF₅, KUOF₅, RbUOF₅ et CsUOF₅

Abstract

Chem. 56,1874Chem. 56, (1978.The oxypentafluoroirranates(V1) MUOF,, where M = NH,, K , R b , Cs, have been synthetized from reaction of UOF, with the animoniu~n or corresponding alkali metal fluoride in liquid SO,. According to X-ray diffraction, Raman and infrared spectroscopy, and from an isoniorphism with the corresponding hexafluorouranates(V) MUFG, two different environ~nents around the ilranii~m atom are observed. In CsUOF, the five fluorine atoms a n d the oxygen around the i~ranium result in a pseudo-octahedral surrounding whereas for the other complexes (M = NH,, K, Rb) cach uranium is surrounded by eight light atoms forming a dodecahedron. In this structure the dodecahedra are linked together by fluorine atoms t o form infinite chains. The UOF,-ion has been characterized by vibrational spectroscopy in the solid state. The proposed assignment, which was made with the assumption of a C,, symmetry of the UOF,-ion, was confirmed by a force constant calculation. From these data and contrary to the values reported for comparable oxypentafluoroanions, the axial fluorine is found to be less ionic than the equatorial ones. Introduction L'ttude des oxypentafluorouranates(V1) MUOF, (M = NO, NH,, K) que nous avions abordte prtctdemment (1,2) a t t t approfondie avec les composCs oh M dtsigne NH,, K, Rb, Cs.

Structural study of the cesium oxypentafluorouranate (VI) CsUOF5

“…2). This is in full agreement with the vibrational spectroscopy study ( 3 ) from which it was concluded that the UOF,-ion has the C , , point group symmetry. On the other hand the force constant calculation has shown the axial fluorine atom (trans to the oxygen atom) to be less ionic in character than the equatorial fluorine atoms.…”

“…The synthesis and characterization of the oxypentafluorouranates(VI) of monovalent cations MUOFj (where M = NO, NH,, K, Rb, Cs) have been described previously (1)(2)(3). According to these studies, a~nollg the alkaline metals studied only CsUOF, has been found to contain the UOF,-ion.…”

“…A comparison of the powder X-ray diffract~on patterns of CsUOF, and CsUF, shows thelr great similarity (2,3). To complete the prevlous stud~es, and, since ~t has been found very challeng~ng to obtaln and keep slngle crystals of CsUOF,, further structural lnvestlgatlons were d~rected towards neutron d~ffraction on a powdered sample.…”

“…The powder neutron diffract~on patterns, the lines of which are llsted 111 Table 1, were recorded at 300 and 4 2 K and the corresponding crystal data were found to be as f o l l o~s Materials and apparatus were as previously described (3). C~UOF,…”

Hydrothermal syntheses and characterization of uranyl tungstates with electro-neutral structural units

“…In these the two most favored uranyl coordinations are [UO 2 F 5 ] 3-, corresponding to a uranyl unit coordinated by five fluorine atoms in the equatorial plane, or [UO 2 F 4 O] 4-, a uranyl pentagonal bipyramid coordinated in the equatorial plane by four fluorine atoms and one oxygen atom. Various uranyl oxy-fluoride inorganic compounds [39][40][41][42] and minerals [43,44] have also been described in the literature. In these compounds it is common for the uranyl unit to have a variable ratio of oxygen to fluorine atoms in the equatorial plane of bypiramids such as [UO 2 being part of the uranyl tungstate sheet.…”