Chemistry of tetravalent actinide phosphates—Part I

The chemistry and crystal structure of phosphates of tetravalent cations, including that of actinides was reviewed several times up to 1985. Later, new compounds were synthesized and characterized. In more recent studies, it was found that some of previously reported phases, especially those of thorium, uranium and neptunium, were wrongly identified. In the light of these new facts an update review and classification of the tetravalent actinide phosphates is proposed in the two parts of this paper. Their crystal structure and some chemical properties are also compared to non-actinide cation phosphates.     

Extraction of actinides in two-phase water-poly(ethylene glycol)—Salt systems in the presence of potassium phosphotungstate

Extraction of actinides has been examined in two-phase aqueous systems based on poly(ethylene glycol) (PEG) from sulfate solutions in the presence of potassium phosphotungstate, which forms strong complexes with ions of tri- and tetravalent transuranium elements. Extraction of these complexes by aqueous PEG solution is complete in contrast to that of penta- and hexavalent actinides. Conditions have been chosen for the separation of actinides in different oxidation states.     

Effect of labile hydrogens on measurement of tritium preserved in hydrogens of cellulose

Various f-elements are separated as anionic complexes from both acidic and alkaline solutions by precipitation with alkylpyridinium salts. The precipitates are also cationic surfactants where the simple counter-ion (e.g. nitrate or chloride) is replaced by the negatively charged complex anion of an actinide or lanthanide. The low solubility of these precipitates is explained by a strong affinity of divalent complex counter-ions of f-elements to the quaternary nitrogen. Precipitations in solutions of nitric acid allow to separate tetravalent f-elements from other metals, in alkaline carbonate solutions tetravalent and hexavalent actinides are precipitated simultaneously. The last procedure yields precipitates, which are very intimate mixtures of hexavalent and tetravalent actinides. This allows to prepare mixed oxides in a simple way.     

Thermoanalytical investigation of layered titanium salts

The investigated materials have similar routes of thermal decomposition; i.e. they lose their crystal water first, then at a higher temperature their structural one. At least the result TiP₂O₇ goes through a phase change at about 1000 K. The amorphous titanium phosphate lost its crystal and structural water at higher temperature than those of crystalline forms. Both α- and γ-titanium phosphates and also their transition metal containing forms have layered structure. In case of α- and γ-forms after the loss of crystal water a phase change occurs which is followed by the decomposition of the molecule. Various transition metals containing γ-titanium phosphates lose their crystal water at the same temperature, with the exception of Ni containing ones. The process is finished in this case at temperature 90 K higher than that of the others. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermoanalytical investigation of crystalline layered hafnium salts

Transition metal containing hafnium phosphates forms has layered monoclinic structure. In general these materials have similar route of thermal decomposition; i.e. they loss their crystal water first then at a higher temperature their structural one. At least the result HfP₂O₇ goes through phase change at about 1000 K. In detail among their thermal decomposition some differences occur. The Mn and Zn containing samples have similar behaviour as pure hafnium phosphate. The Cu and Ni containing materials have an additional exo-process connected with the transition metal oxide forms. In case of Co containing sample similar to that of Zn containing one (but very weak) processes were observed.     

Surface basicity on bulk modified phosphorus alumina through different synthesis methods

Bulk modified phosphorus alumina samples were prepared by gel method (GPA) and hydrolysis of phosphide aluminum (HPA). The γ-Al(2)O(3) impregnated by phosphates precursor (IPA) was also compared. The basicity of the samples has been investigated through the CO(2) adsorption/desorption processes by in situ DRIFT and temperature programmed desorption experiments. It was found that the surface basicity can be adjusted by different location of phosphates species. For the GPA sample, the phosphates species tends to be located in the grain boundaries as they were not stable enough to overcome the structure rearrangement at high temperatures. In contrast, phosphorus was stably anchored in the crystal lattice of HPA sample. Considering the synthesis process of HPA samples, phosphorus changed its valence state from P(-3) to P(+5) and migrated from anion to cation sites. The anion vacancies left in the lattice facilitated the formation of unsaturated oxygen ions and results in the enhanced basicity.     

AN EPR STUDY OF π-CATION RADICALS IN DINUCLEOSIDE PHOSPHATES AND DNA PRODUCED BY PHOTOIONIZATION

In this work we have produced the π-cation radicals of a number of nucleotides, dinucleoside phosphates, and DNA in aqueous glasses (8M NaCIO₄) by photoionization and investigated these species by EPR spectroscopy. Results found for nucleotides and dinucleoside phosphates containing one type of DNA base, e.g. TpT, GpG, or dApdA, were used in the analysis of spectra found for mixed dinucleoside phosphates, e.g. TpdG. For TpdG and TpdA in neutral glasses photoionization takes place from the purine base and no transfer of charge to the pyrimidine base is found. In basic conditions both the adenine and thymine π-cations are observed in TpdA. In both neutral and basic conditions the results found for mixed dinucleoside phosphates containing guanine show that the guanine cation is formed preferentially by photolysis. This result was found to extend to DNA. Photolysis of DNA in 8M NaC1O₄ produced principally the guanine cation. Computer simulations using parameters determined by other workers from a study of γ-irradiated oriented DNA closely match the spectrum found in this work attributed to the guanine cation in dinucleoside phosphates and DNA. This work thus confirms the presence of the guanine cation in γ-irradiated DNA.     

Structural Periodicity in the Coordination Chemistry of Aqueous Pu(IV) Sulfates

Extended X-ray absorption fine structure measurements have been conducted on solutions of Pu(IV) with varying concentrations of sulfate anion in aqueous solution. Data support the periodic progression to primarily bidentate sulfate coordination about An(IV) centers when moving heavier in the actinides. This observation is attributed to the increase in Lewis acidity of the tetravalent actinides across the series, a consequence of the filling of the 5f orbitals and the actinide contraction. Though the changes in the chemical formation energies of the An(IV) complexes between Th and Pu are small, it is these small energetic differences that are critical to understanding how to effect more efficient and effective chemical separations among isovalent metal ions.     

Synthesis of functional monolayer surfaces for rapid radiometric determination of plutonium

Glass or silicon substrates functionalized with a monolayer of carbamoylmethylphosphonate (CMP) ligands effectively bind tetravalent actinides from optimized mineral acid solutions to enable rapid, high quality radiometric assay by alpha spectrometry. The observed alpha spectra compare favorably with the highest quality electroplated samples. The CMP-functionalized surfaces have been used to develop simplified analytical methods to determine plutonium from complex mixtures.     

Determination of U(IV) and U(VI) by ion chromatography-inductively coupled plasma mass spectrometry and its application to kinetic studies

The ions normally formed by actinides in aqueous solutions by the oxidation states III-VI are M3-, M4+, MO2+ and MO2(+2), respectively. Oxidation state representatives such as Am3+, Th4+, NpO+ and UO+, which resist oxidation state changes, were used to investigate a method to separate the oxidised species (MO2 and MO2(2+)) from the reduced species (M3+ and M4+). With this method the hexavalent state of uranium could be separated from the tetravalent state of uranium in aqueous media in less than 8 min. Uranium concentrations down to 10(-9) M could be analysed without changing the redox composition during the separation. The oxidation kinetics of the tetravalent uranium for different hydrochloric acid concentrations was investigated. The measurements showed good agreement with values found in the literature, although the uranium concentrations were one million times lower.     

Pentavalent Neptunyl ([O≡Np≡O]<Superscript>+</Superscript>) Cation–Cation Interactions in Aqueous/Polar Organic Mixed-Solvent Media

Bonding interactions between polyvalent cations and oxo-anions are well known and characterized by predictably favorable Gibbs energies in solution-phase coordination chemistry. In contrast, interactions between ions of like charge are generally expected to be repulsive and strongly influenced by cation solvation. An exception to this instinctive rule is found in the existence of complexes resulting from interactions of pentavalent actinyl cations ([O≡An≡O]⁺) with selected polyvalent cations. Such cation–cation complexes have been known to exist since the 1960s, when they were first reported by Sullivan and co-workers. The weak actinyl cation–cation complex, resulting from a bonding interaction between a pentavalent linear dioxo actinyl cation donor and hexavalent actinyl or trivalent/tetravalent metal cation acceptor, has been most commonly seen in media in which water activities are reduced, principally highly-salted aqueous media. Such interactions of pentavalent actinides are of relevance in ongoing research that focuses on advanced nuclear fuel processing systems based on the upper oxidation states of americium. This investigation focuses on exploring the thermodynamic stability of complexes between selected highly-charged metal cations (Al³⁺, Sc³⁺, Cr³⁺, Fe³⁺, In³⁺ and \( {\text{UO}}_{2}^{2 + } \)) and the pentavalent neptunyl cation (\( {\text{NpO}}_{2}^{ + } \), whose coordination chemistry is similar to that of \( {\text{AmO}}_{2}^{ + } \) while exhibiting significantly greater oxidation state stability) in aqueous–polar organic mixed-solvents. The Gibbs energies for the cation–cation complexation reactions are correlated with general features of electrostatic bonding models; the \( {\text{NpO}}_{2}^{ + } \cdot {\text{Cr}}^{3 + } \) complex exhibits unexpectedly strong interactions that may indicate significant covalency in the cation–cation bonding interaction.     

New hydrothermal synthesis and structure of Th2(PO4)2(HPO4).H2O: the first structurally characterized thorium Hydrogenphosphate

Th(2)(PO(4))(2)(HPO(4)).H(2)O was synthesized under wet hydrothermal conditions starting from a mixture of H(3)PO(3) and Th(NO(3))(4).5H(2)O. The crystal structure was solved by powder X-ray diffraction data. The unit cell parameters are a = 6.7023(8) Angstroms, b = 7.0150(8) Angstroms, c = 11.184(1) Angstroms, beta = 107.242(4) degrees, space group P2(1), and Z = 2. The structure consists of layers of both thorium atoms and PO(4) groups, alternating with a layer formed by HPO(4) entities and water molecules. By thermal treatment, this compound turns into Th(4)(PO(4))(4)P(2)O(7), a ceramic already described in the field of the immobilization of tetravalent actinides.     

Sequential separation of actinides and lanthanides by extraction chromatography using a CMPO-TBP/XAD7 column

CMPO/TBP sorbed on Amberlite XAD7 resin was used for the separation of actinides and lanthanides from nitric acid solutions by extraction chromatography. The distribution ratios of actinides and lanthanide fission products (Ce, Eu) as a function of acid concentration and some complexing agents were determined. In strong HNO₃ medium (>1 mol/l) the tri-, tetra- and hexavalent actinides as well as the lanthanides have shown great affinity for the CMPO/TBP/XAD7 sorbent. The same behavior was found in HCl medium except for trivalent actinides and lanthanides which show lower distribution values in the same acid range. The effect of some complexing agents as DTPA and ammonium oxalate were also investigated. In DTPA only hexavalent actinides showed higher distribution value. On the basis of these differences, an alternative procedure for actinide-lanthanide separation and actinides from each other is proposed.     

Extraction and coordination behavior of diphenyl hydrogen phosphine oxide towards actinides

Extraction behavior of some selected actinides like U(VI), Th(IV), and Am(III) was investigated with three different H-phosphine oxides, viz. diphenyl hydrogen phosphine oxide (DPhPO), dihexyl hydrogen phosphine oxide (DHePO) and diphenyl phosphite (DPP). The H-phosphine oxides exhibited a dual nature towards the extraction of actinides where the ligand not only extracts the metals by cation exchange but also by coordination with the phosphoryl group at lower and higher acidic concentrations, respectively. Among all ligands employed, DPhPO showed highest extraction with actinides with a substituent dependent trend as follows: DPhPO > DHePO > DPP. This trend emphasizes the importance of substituents around the phosphine oxide towards their extraction of actinides. The coordination behavior of DPhPO was studied by investigating its corresponding complexes with Th(NO₃)₄ and UO₂(NO₃)₂. The metal complexes of these actinides were characterized using FT-IR, ¹H and ³¹P NMR spectroscopic techniques. Density Functional Theory (DFT) calculations were also performed to understand the electronic and geometric structure of the ligand and the corresponding metal complexes.     

APPLICATIONS OF CERIUM BIS （MONOMYRISTY—LPHOSPHATE）ADSORBENT TO REVERSED PHASE LIQUID CHROMATOGRAPHY

The tetravalent metal salts of monoalkyl phosphates [M(O3POR)2]are a new kind of stationary phases of Chromatography-homogeneous bonded phases.This paper deals with the application of cerium bis(monomyristylphosphate)as support to reversed phase liquid chromatography.The results show that the best mobil phase is CH3CN:H2O=95:5.The good separation to the mixture containing six aromatic hydrocarbons and the determination of naphthalene in a group samples have been achieved.The regression analysis shows that detect limits,linearities and precision for six aromatic hydrocarbons are good.     

Stability constants of tervalent actinide and lanthanide sulfate complexes in aqueous solutions

The stability constants of 1: 1 sulfate complexes (ion pairs) at 298 K are approximately calculated for all tervalent actinides and lanthanides, scandium, yttrium, and for alkali, earth-alkali, and some bivalent transition metals in aqueous solutions. The method used consists in integrating the function of the ligand distribution density with respect to a cation and allows either only solvent-separated ion pairs or all types of ion pairs to be taken into account in the calculation of constants. The dominance of solvent-separated ion pairs in infinitely dilute solutions is shown for lanthanides, actinides, and for the majority of the considered metals by comparison with experimental data.     

Oligomers Intermediates in Between Two New Distinct Homonuclear Uranium(IV) DOTP Complexes**

Two new aqueous U^IV complexes were synthesized by the interaction between the tetravalent uranium cation and the (1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetra(methylene phosphonic acid) (DOTP) macrocyclic ligand. Two distinct homonuclear complexes were identified; the first was characterized by X-ray crystallography as a unique “out-of-cage”, [U(DOTPH₆)₂] complex, in which the U^IV cation is octa-coordinated to 4 phosphonic arms from each ligand in a square anti-prism geometry, with a C₄ symmetry. The second is the “in-cage” [U(DOTPH₄)] complex, in which the tetravalent cation is located between the macrocycle O₄ and N₄ planes. With the help of UV-Vis absorption, ¹H/³¹P NMR, ATR-IR, and MALDI-TOFMS analytical techniques, the chemical interchange between both species is presented. It is shown that the one-way transition is governed by the formation of a multiple number of soluble oligomeric species consisting of varied stoichiometric ratios of both characterized homonuclear complexes.     

Tetravalent Zr<Superscript>4+</Superscript> ion conduction in NASICON-type phosphate solids

The ionic conduction of mono-, di-, and trivalent ions in solids is popular in solid state science and the next target ion species to migrate in solids are tetravalent ions. Here, a tetravalent cation conductor which shows high conductivity, comparable to the conductivity range of the representative divalent oxide anion conductors, was artificially designed by strictly selecting the constituent elements and the structure. The tetravalent ion conducting solid electrolyte proposed here shows considerable high ion conductivity and promising applications, such as in rechargeable batteries and chemical sensors for global environmental monitoring, are greatly expected. Electronic Publication     

Extraction of tri- and tetravalent actinides with dihexyl N,N-diethylcarbamoylmethyl phosphonate (DHDECMP) and TBP from nitric acid solutions

Extraction of trivalent (Pu³⁺, Am³⁺, actinides and Eu³⁺, a representative of lanthanides) and tetravalent (Np⁴⁺ and Pu⁴⁺) actinides has been studied with dihexyl N,N-di-ethylcarbamoylmethyl phosphonate (DHDECMP) in combination with TBP in benzene from 2M nitric acid. The stoichiometries of the species extracted were found to be M(NO₃)₃·(3–n) TBP·n DHDECMP (for trivalent ions) and M(NO₃)₄·(2–n) TBP·n DHDECMP (for tetravalent ions) by the slope ratio method. The extraction constants evaluated (from the distribution data) indicate that for tetravalent ions (with solvation number two) the extraction constant increases when TBP (Kh=0.17) molecules are successively replaced by more basic DHDECMP (Kh=0.34) molecules. However, for trivalent ions (with solvation number three) when TBP molecules are totally replaced by DHDECMP molecules stereochemical factors appear and instead of increase, a substantial decrease in extraction constants is observed for Eu³⁺ and Am³⁺, a lesser decrease being observed for Pu³⁺ (larger ion).     

具有新结构类型的化合物Csln[PO3(OH)]2的合成与结构

水热法合成了新结构类型化合物CsIn[P03(0H)]2,并通过单晶X-射线衍射表征结构.标题化合物空间群为P121/c1(No.14),晶体学参数为:M=439.69,mP56,a=0.532 86(6)nm,b=0.91653(7)nm,c=1.478 39(14)nm,β=93.849(9).,V=0.7204(1)nm3,Z=4,Dx=4.054 g·cm-3,μ=8.713 mm-1,F(000)=800,R1= 0.0325,wR2=0.0874.在该化合物中,2个In06八面体和4个PO4四面体形成交连的六元环柱,并沿a轴方向形成近六方密堆积并连接成Cs+离子占据的十二元环结构隧道,六元环和十二元环连接构筑了三维网络结构.与类似化学计量比化合物Na2In2[PO3(0H)]4·H2O比较,标题化合物中十二元环的形成明显取决于隧道阳离子的大小,其拓扑构造可看作扩展的6,3-网格连接,化合物RbIn[PO3(0H)]2与之同构.