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A series of uranyl and lanthanide (trivalent Ce, Nd) mellitates (mel) has been hydrothermally synthesized in aqueous solvent. Mixtures of these 4f and 5f elements also revealed the formation of a rare case of lanthanide-uranyl coordination polymers. Their structures, determined by XRD single-crystal analysis, exhibit three distinct architectures. The pure lanthanide mellitateLn2(H2O)6(mel) possesses a 3D framework built up from the connection of isolated LnO6(H2O)3polyhedra (tricappedtrigonal prism) through the mellitate ligand. The structure of the uranylmellitate (UO2)3(H2O)6(mel) 11.5H2O is lamellar and consists of 8-fold coordinated uranium atoms linked to each other through the organic ligand giving rise to the formation of a 2D 36 net. The third structural type, (UO2)2Ln(OH)(H2O)3(mel) 2.5H2O, involves direct oxygen bondings between the lanthanide and uranyl centers, with the isolation of a heterometallicdinuclear motif. The 9-fold coordinated Ln cation, LnO5(OH)(H2O)3,is linked to the 7-fold coordinated uranyl (UO2)O4(OH) (pentagonal bipyramid) via one μ2-hydroxo group and oneμ2-oxo group. The latter is shared between the uranyl bonding (U-O = 1.777(4)/1.779(6) Å) and a long Ln-O bonding (Ce-O = 2.822(4) Å; Nd-O = 2.792(6) Å). This unusual linkage is a unique illustration of the so-called cation-cation interaction associating 4f and 5f metals. The dinuclear motif is then further connected through the mellitate ligand, and this generates organic-inorganic layers that are linked to each other via discrete uranyl (UO2)O4 units (square bipyramid), which ensure the three-dimensional cohesion of the structure. The mixed U-Ln carboxylate is thermally decomposed from 260 to 280 ÅC and then transformed into the basic uranium oxide (U3O8) together with U-Ln oxide with the fluorite structural type ("(Ln,U)O2"). At 1400 °C, only fluorite type "(Ln,U)O2" is formed with the measured stoichiometry of U0.63Ce0.37O2 and U0.60Nd0.40O2-δ. [ABSTRACT FROM AUTHOR]

An uranyl isophthalate has been hydrothermally synthesized at 200 °C for 24 h, from a mixture of uranyl nitrate, isophthalic acid, and hydrazine in water. It was characterized by single-crystal analysis [triclinic, P¯1, a = 7.3934(3) Å, b = 13.3296(5) Å, c = 15.4432(5) Å, α = 111.865(2)°, β = 90.637(2)°, γ = 104.867(2)°, V = 1355.49(9) Å3] and different spectroscopic techniques (Raman, IR-ATR, UV-visible). The 3D structure of the phase (UO2)8O2(OH)4(H2O)4(1,3-bdc)4·4H2O (1,3-bdc = 1,3-benzenedicarboxylate) reveals octanuclear units based on the association of 7-fold coordinated uranyl cations (pentagonal bipyramid) involving a rare case of cation-cation interaction together with edge-sharing polyhedral connection mode. UV-visible absorption spectroscopy confirmed that uranium was only involved in the structure as uranyl forms (excluding the presence of tetravalent or pentavalent uranium). Additionally, μ-Raman and IR-ATR experiments allowed assigning four uranyl contributions to the four types of uranyl entities in the structure, in agreement with the XRD analysis. [ABSTRACT FROM AUTHOR]

Crystallized powder of dihydroxide zirconium oxalate Zr(OH) 2 (C 2 O 4 ) ( ZrOx ) was obtained by precipitation and the structure determined from powder X-ray data. The three-dimensional (3D) framework observed in ( ZrOx ) results from the interconnection of zirconium hydroxide chains 1 ∞ [Zr(OH) 2 ] 2+ and zirconium oxalate chains 1 ∞ [{Zr(C 2 O 4 )} 2+ ]. Single crystals of (H 11 O 5 ) 2 [Zr 2 (C 2 O 4 ) 5 (H 2 O) 4 ] ( H2Zr2O5 ) were obtained by evaporation. The structure contains dimeric anions [Zr 2 (C 2 O 4 ) 5 (H 2 O) 4 ] 2- connected through hydrogen bonds to hydroxonium ions (H 11 O 5 ) + to create a 3D supramolecular framework. The addition of ammonium or alkali nitrate led to the formation of single crystals of Na 2 [Zr(C 2 O 4 ) 3 ]·2H 2 O ( Na2ZrOx3 ), M(H 7 O 3 )[Zr(C 2 O 4 ) 3 ]·H 2 O, M = K ( KHZrOx3 ), M = NH 4 ( NH4HZrOx3 ), M(H 5 O 2 ) 0.5 (H 9 O 4 ) 0.5 [Zr(C 2 O 4 ) 3 ], M = Rb ( RbHZrOx3 ), and M = Cs ( CsHZrOx3 ). For the five compounds, the structure contains ribbons 1 ∞ [{ZrOx 3 } 2- ] formed by entities Zr(C 2 O 4 ) 4 sharing two oxalates. In ( Na2ZrOx3 ), the shared oxalates are in cis positions and the chain 1 ∞ [Zr-Ox] is stepped with a Zr-Zr-Zr angle of 98.27(1)°. In the other compounds, the shared oxalates are in trans positions and the chains 1 ∞ [Zr-Ox] are corrugated with Zr-Zr-Zr angles in the range 140.34(1)-141.07(1)°. In the compounds ( MHZrOx3 ), the cohesion between the ribbons is ensured by the alkaline or ammonium cations and the hydroxonium ions (H 7 O 3 ) + for M = K, NH 4 , (H 5 O 2 ) + , and (H 9 O 4 ) + for M = Rb and Cs. During the thermal decomposition of the alkaline-free zirconium oxalates ( ZrOx ), ( H2Zr2Ox5 ), and ( NH4HZrOx3 ), the formed amorphous zirconia is accompanied by carbon; the oxidation of carbon at about 540 °C to carbon dioxide is concomitant with the crystallization of the stabilized tetragonal zirconia., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)