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A series of isostructural oxalates of Th, U, Np, and Pu have been synthesized. The crystal structure of {C(NH(2))(3)}(4)[An(C(2)O(4))(4)]·2H(2)O comprises infinite [An(C(2)O(4))(4)](4n-) chains, guanidinium cations and water molecules. Each An atom is connected to five oxalate anions, two of which act as bridging tetradentate ligands, while the other three function as terminating bidentate ligands. Electron and IR spectra of the compounds as well as the results of thermal analysis correlate with their structure. An actinide contraction effect is demonstrated by a decrease in the An-O interatomic distances and the volumes of An atom coordination polyhedra and Voronoi-Dirichlet polyhedra. Ten-coordinate An oxalates are discussed in terms of continuous shape measures approach.

This study concerns the formation of complexes with actinides at oxidation state +IV, from Th to Am, through a lacunary heteropolyanion ligand P(2)W(17)O(61)(10-). The preparation of original single crystals of complexes with 1:2 stoichiometry provided structural data through single-crystal X-ray diffraction for the entire An(IV) series. An(IV) atoms in these complexes have a coordination number of 8, and their coordination polyhedron is a distorted square antiprism. The data were used to compute a mean (An-O) interatomic distance for each actinide. When the interatomic distance is plotted versus the inverse ionic radius of these tetravalent actinides, it appears that the simple electrostatic model is not suitable for Am(IV) and Pu(IV), although this trend must be confirmed by further investigation with other examples from the An(IV) series.

SummaryThe interactions of Pu(N) and Pu(VI) in alkaline media with some metal hydroxides and oxides commonly found in Hanford Site tank wastes were studied. The properties of mixed hydroxide systems of Pu(IV) with various metal ions mi@), Fe(III), C o o , Al(m), Cr(m>, Zr(IV), La(IlI), and U(VI)] were investigated at variable component ratios using physicalchemical methods. The interactions of P u O with Al(lII), Fe(III), and Cr(IlI) also were studied.It was shown by infrared (IR) spectroscopy that, except for the system Pu(IV)-Ni(II), Pu(IV) interacts with all the listed metal ions and affects their interatomic bonding. The locations of IR absorption bands of the mixed hydroxides change irregularly compared with the spectra of pure components, with change in the Pu:metal mole ratio of from 1:lO to 1O:l. The changes occur both for the valent and deformation vibration bands of hydroxyl ions and water at 3600 to 3100 and 1750 to 1250 cm-' and for the vibrations of metal-oxygen (M-0) bridging bonds in the range of 1050 to 850 cm-'. In the Pu(IV)/Ni(II) system, the IR spectra are equivalent to the sum of the individual components precipitated separately from alkaline solution.The separate precipitation of h(N) hydrous oxide and Ni(OH), upon adding NaOH solution to acidic solution containing both Pu(N) and Ni(II) nitrate was confirmed by studying the dissolution rate of the resulting precipitate in 3 M HCl at 60°C. No difference in plutonium dissolution behavior was found for pure PuO,-xH,O and the products obtained by alkaline precipitation of 1: 1 mole ratio Pu(N):Ni(II) mixtures, aged for 1 hour at 70"C, over a wide range of NaOH concentrations. Similar results were obtained for the Pu(IV)-Al(III) system. Only trace amounts of aluminum were detected in pUO,.xl&O precipitates formed even in relatively dilute NaOH solutions.

Preparation, crystal structure and properties revealed through IR and visible absorption spectroscopy study of Np(V,VI), Pu(VI) compounds formed with pertechnetate anions are reported. Spectrophotometric study of Np(V) and Pu(VI) in NH