Crystal Growth and First Crystallographic Characterization of Mixed Uranium(IV)–Plutonium(III) Oxalates

Abstract

The mixed-actinide uranium(IV)-plutonium(III) oxalate single crystals (NH4)0.5[Pu(III)0.5U(IV)0.5(C2O4)2·H2O]·nH2O (1) and (NH4)2.7Pu(III)0.7U(IV)1.3(C2O4)5·nH2O (2) have been prepared by the diffusion of different ions through membranes separating compartments of a triple cell. UV-vis, Raman, and thermal ionization mass spectrometry analyses demonstrate the presence of both uranium and plutonium metal cations with conservation of the initial oxidation state, U(IV) and Pu(III), and the formation of mixed-valence, mixed-actinide oxalate compounds. The structure of 1 and an average structure of 2 were determined by single-crystal X-ray diffraction and were solved by direct methods and Fourier difference techniques. Compounds 1 and 2 are the first mixed uranium(IV)-plutonium(III) compounds to be structurally characterized by single-crystal X-ray diffraction. The structure of 1, space group P4/n, a = 8.8558(3) Å, b = 7.8963(2) Å, Z = 2, consists of layers formed by four-membered rings of the two actinide metals occupying the same crystallographic site connected through oxalate ions. The actinide atoms are nine-coordinated by oxygen atoms from four bidentate oxalate ligands and one water molecule, which alternates up and down the layer. The single-charged cations and nonbonded water molecules are disordered in the same crystallographic site. For compound 2, an average structure has been determined in space group P6/mmm with a = 11.158(2) Å and c = 6.400(1) Å. The honeycomb-like framework [Pu(III)0.7U(IV)1.3(C2O4)5](2.7-) results from a three-dimensional arrangement of mixed (U0.65Pu0.35)O10 polyhedra connected by five bis-bidentate μ(2)-oxalate ions in a trigonal-bipyramidal configuration.

From uranium(IV) oxalate to sintered UO 2 : Consequences of the powders' thermal history on the microstructure

“…Among these precursors, and even if inorganic or metal-organic compounds were studied for long to prepare actinide oxides [14,15], several recent studies particularly pointed out the benefits induced by the use of oxalate precursors (see for example the recent review by Abraham et al and the references therein [16]). They particularly provide quick, quantitative and homogenous precipitation of cations from aqueous mixtures, and offer the possibility to incorporate simultaneously actinides presenting different oxidation states [17,18]. Moreover, the corresponding oxides are easily obtained through a heating conversion step [19,20].…”

Spectroscopic Studies and Crystal Structures of Double Thorium(IV) Oxalates with Sodium Ions

“…A Pu IV oxalate with a hydroxy group, KPu(C 2 O 4 ) 2 (OH) · 2H 2 O, was characterized 27. More recently, a mixed U IV –Pu III oxalate with a hexagonal structure was also reported 28…”

Multiscale structural characterizations of mixed U(iv)–An(iii) oxalates (An(iii) = Pu or Am) combining XAS and XRD measurements

“…The diffraction patterns are very similar and characteristic of the hexagonal M 2+x U IV 2−x An/Ln III x (C 2 O 4 ) 5 •nH 2 O compounds. 20,24 It is interesting to note that the lattice parameters evolve along the actinide/lanthanide series ( Table 2). The decrease in the lattice parameters from Ce(III) to Gd(III) for the hexagonal structure is in agreement with the decreasing ionic radii along the lanthanide series 22 (Table 2) 10%).…”

“…Up until now, there is only one structural determination from single-crystal X-ray diffraction data concerning mixed actinide(IV)-actinide(III) oxalate compounds. 20 In many works U(IV)-Ln(III) systems are considered as good structural analogs of An(IV)/An(III) systems due to their similar ionic radii. [21][22][23] Consequently, the structure of precipitated actinide oxalates 14,16,18 has often been identified by comparison with the structural data of a three mixed U(IV)-Ln(III) oxalate series, named hexagonal, triclinic and tetragonal, with the formula M 2+x U IV 2−x Ln III x -(C 2 O 4 ) 5 •nH 2 O for the first and M 1−x Ln III 1−x U IV x (C 2 O 4 ) 2 •nH 2 O for the last two, [24][25][26] where M is a monovalent cation.…”