Structural study of the cesium oxypentafluorouranate (VI) CsUOF₅

Abstract

Powder samples of cesium oxypentafluorouranate(V1) were studied by both neutron diffraction and 19F broad line nuclear magnetic resonance.CsUOF, crystallises with the R3 space group, ~i t h the parameters a = 5.41 i 0.01 A ; x = 95-34' & 5'. The structure, which \\'as found to be unchanged at temperatures as low as 4.2 K, was interpreted by a statistical occupation of six-fold equivalents sites, the occupation rate being 1'6 and 5'6 for oxygen and fluorine, respectively. The nmr study showed that the disorder corresponding to this structure was of dynamic type, and that the UOF,-ions were in isotropical rotation. The motion is observable at temperatures as low as 223 K with a characteristic time s equal to 3 x 1 0 -9 at 266 K. On the other hand, it was also shown through this nmr study that the point symmetry of the UOF,-ion corresponds to the C,, group, with the axial fluorine being more covalent than the eq~~atorial ones. Consistency of the diffraction and nmr results is discussed.Can. J. Chem. 56. 2546 (1978).L'oxvoentafluorouranate(V1~ de cesium CsUOF, a ete etudit sur poudre par diffraction * .~, neutronique et resonance magnitique n~~cleaire du 19F en large bande.CsUOF, cristallise dans le groupe spatial R3 avec les parametres cr = 5.41 i 0.01 A ; a = 95'34' i 5'. I1 n'y a pas de changenient de structure jusqu'a 4.2 K , et celle-ci s'interprete par une occupation statistique de sites a 6 equivalents avec un taux d'occupation respectivernent egal a 1,'6 et 5,'6 pour l'oxygene et le fluor. L'etude rmn nlontre que le dtsordre correspondant cette structure est de type dynamique et que les ions UOF,-sont en rotation isotrope. Le mouvement peut-@tre observe jusqu'a 223 K, avec un temps caracteristique r de 3 x 10-5 s a 266 K. La rmn montre parailleurs, que l'ion UOF,-possede une symetrie ponctuelle correspondant au groupe C4L, avec uil fluor axial plus covalent que les fluors equatoriaux. La coherence des rCsultats structuraux obtenus par diffraction et par rlnn est discutee. lntrodnctionThe synthesis and characterization of the oxypentafluorouranates(VI) of monovalent cations MUOFj (where M = NO, NH,, K, Rb, Cs) have been described previously (1-3). According to these studies, a~nollg the alkaline metals studied only CsUOF, has been found to contain the UOF,-ion. The structure of this ion was further studied by neutron diffraction and 19F nuclear magnetic resonance on a poadered sample. Data from these investigations are presently reported. Experimental Part Results and Discussion CI j r t a l l o g r a~~l~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~...

Metal–ligand multiple bonding in uranium: structure and reactivity

“…Complexes with the formula M[UOF 5 ] (M = NH 4 , K, Rb, Cs) are also known, but little characterization data for these compounds is available. 129,130 The mixed-valent uranium 131 This complex can also be viewed as a uranyl analogue, a comparison that is more apparent considering the recent syntheses of the trans-bis(imido) complexes of uranium (vide infra). It exhibits a U-O bond length of 1.838(5) A ånd a O-U-N imido angle of 161.2(2) • (Fig.…”

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

“…Les angles sont pris kgaux h 90' et les distances interatomiques choisies sont dkduites des calculs faits A partir des spectres de diffraction de neutrons soit U-0 = S = 1.80A, U-F,, = r = UF,, = R = 2.09 A (22 (27) a un caracttre de covalence infkrieur ou proche de celui de UF, (31) tandis que les quatres liaisons du plan Cquatorial ont un caracttre ionique proche de celui trouvk pour I'ion UF,- (32). On identifie bien, deux types de liaisons pour UOF,-avec une liaison axiale plus covalente que I1Cquatoriale.…”

Two new uranyl fluoride complexes with UVIO–alkali (Na, Cs) interactions: Experimental and theoretical studies

“…Generally, uranium fluorides are of particular importance because they are typical nuclear fuels in molten salt based reactors and fissile uranium isotope enrichment. Hence, the chemistry about uranium fluorides is well studied ranging from experiments [2][3][4][5][6][7][8][9][10][11] to theoretical calculations. [12][13][14][15][16] The rigorously linear OLULO covalent bonds originating from the hybridization of metal 5f/6d and oxygen 2p orbitals always exhibit large chemical inertness, 17 so donor atoms of ligands typically bond to uranyl dication in equatorial planes, predominantly forming sheet type structures, [18][19][20] as well as clusters, [21][22][23] chain, 24,25 and 3D compounds.…”