Synthesis and properties of actinide dimolybdate complexes M<Subscript>2</Subscript>[AnO<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript>]·H<Subscript>2</Subscript>O (M = Rb,Cs; An = Np,Pu)

New Np(VI) and Pu(VI) dimolybdates Rb₂NpO₂(MoO₄)₂·H₂O (I), Cs₂NpO₂(MoO₄)₂·H₂O (II), Cs₂PuO₂(MoO₄)₂·H₂O (III), and Rb₂PuO₂(MoO₄)₂·H₂O (IV) were synthesized under hydrothermal conditions. The crystal structures of the compounds were determined, and their absorption spectra in the UV, visible, and IR ranges were measured. The compounds crystallize in the monoclinic system. Their crystal structure is based on [AnO₂(MoO₄)₂]_n^2n– anionic layers (An = Np, Pu) formed by (AnO₂)O₅ pentagonal bipyramids and MoO₄ tetrahedra, sharing common vertices. Each An atom in the layer is bonded to other five An atoms via MoO₄ tetrahedra with the formation of a 4343² network. The effect of the ionic radius of the outer-sphere cation on the parameters of the crystal structure and features of the absorption spectra is discussed.     

Synthesis,crystal structure,and properties of new actinide(VI) arsenates (H<Subscript>3</Subscript>O)[(AnO<Subscript>2</Subscript>)(AsO<Subscript>4</Subscript>)]·3H<Subscript>2</Subscript>O (An = U,Np, Pu)

Previously unknown arsenates of hexavalent U, Np, and Pu, (H₃O)[(UO₂)(AsO₄)]·3H₂O (I), (H₃O)· [(NpO₂)(AsO₄)]·3H₂O (II), and (H₃O)[(PuO₂)(AsO₄)]·3H₂O (III), were synthesized under hydrothermal conditions. The crystal structure of the compounds was determined, and their absorption spectra were measured. The compounds crystallize in tetragonal space group P4/nmm.     

Crystal structure of a Np(V) sesquioxalate,Na<Subscript>4</Subscript>(NpO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>3</Subscript>·2H<Subscript>2</Subscript>O

The crystal structure of a previously unknown Np(V) sesquioxalate, Na₄(NpO₂)₂(C₂O₄)₃·2H₂O was studied. The crystal structure consists of neptunyl(V) cations, sodium cations, oxalate anions, and water molecules of crystallization. Neptunyl(V) cations and oxalate ions form anionic chains [(NpO₂)₂(C₂O₄)₃] _n ^4n? . The coordination polyhedron (CP) of Np (pentagonal bipyramid) contains two apical “yl” oxygen atoms and five equatorial O atoms of three oxalate ions. The CP of Na(1) and Na(2) cations are combined through the common edges into zigzag chains in the [010] direction. Two independent oxalate ions are tridentate and tetradentate ligands.     

Crystal structure of U(VI) phthalate dihydrate [UO<Subscript>2</Subscript>(OOC)<Subscript>2</Subscript>C<Subscript>6</Subscript>H<Subscript>4</Subscript>•H<Subscript>2</Subscript>O]•H<Subscript>2</Subscript>O

Crystalline uranyl phthalate dihydrate was prepared by hydrothermal method, and its crystal structure was determined. The crystal structure consists of infinite chains [UO₂LH₂O]_n coupled in bands [(UO₂)₂L₂(H₂O)₂]_n [L = C₆H₄(COO)₂], between which water molecules of crystallization are located. The coordination polyhedron of uranium atoms is a pentagonal bipyramid with the equatorial plane formed by oxygen atoms of three phthalate ions and coordinated water molecule. The U-O bond length in the UO ₂ ²⁺ cations is 1.766 . The coordination capacity of the ligands is 4. Anions are bidentately coordinated to uranium atoms to form seven-membered rings. Being bridging ligands, phthalate ions combine the neighboring uranium atoms into chains through one carboxy group, and the chains into bands, through the other carboxy group.Translated from Radiokhimiya, Vol. 46, No. 6, 2004, pp. 513–515.Original Russian Text Copyright © 2004 by Charushnikova, Krot, Starikova.     

Synthesis and Structure of Mixed Cromate–Nitrate Complexes of Hexavalent Actinides, [(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>N][(AnO<Subscript>2</Subscript>)(CrO<Subscript>4</Subscript>)(NO<Subscript>3</Subscript>)] (An = U,Np, Pu)

Mixed-anion compounds of the general composition [(CH₃)₄N][(AnO₂)(CrO₄)(NO₃)], where An = U, Np, and Pu, were synthesized and structurally characterized. The structural motif of these compounds is based on anionic ribbons of the composition [AnO₂(NO₃)(CrO₄)]_n^n–, consisting of seven-vertex An polyhedra linked via oppositely oriented CrO₄ tetrahedra and NO₃ groups acting in the An polyhedra as terminal bidentate ligands. Every four anionic ribbons form channels oriented along b-axis. Tetramethylammonium cations linked with the O atoms of the ribbons by hydrogen bonds are located in these channels. Actinide contraction is observed in the series U–Np–Pu. It is manifested in a regular decrease in the interatomic distances in the An polyhedra, in parameters b and c, and in the unit cell volume.     

Crystal structure of a Pu(VII) potassium salt,K<Subscript>3</Subscript>PuO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>·2H<Subscript>2</Subscript>O

A new Pu(VII) compound, K₃PuO₄(OH)₂·2H₂O, was synthesized, and its structure was studied by single crystal X-ray diffraction. This compound is isostructural to the previously described K₃NpO₄(OH)₂·2H₂O. The structure of the latter compound was redetermined to obtain more precise interatomic distances in the NpO₂(OH) ₂ ^3? anion. Changes in An-O bond lengths in the tetragon-bipyramidal coordination polyhedron of the compounds K₃AnO₄(OH)₂·2H₂O in going from Np(VII) to Pu(VII) were considered.     

Synthesis and Structure of the Np(VII) Complex with Guanidinium,Li[C(NH<Subscript>2</Subscript>)<Subscript>3</Subscript>]<Subscript>2</Subscript>[NpO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]·6H<Subscript>2</Subscript>O

The previously unknown Np(VII) compound Li[C(NH₂)₃]₂[NpO₄(OH)₂]·6H₂O (I), containing organic cations, was synthesized and studied by single crystal X-ray diffraction. In contrast to the relatively numerous structurally characterized salts of [NpO₄(OH)₂]^3– anions with Na⁺, K⁺, Rb⁺, and Cs⁺ cations, which were prepared only from strongly alkaline media, crystals of I were isolated from solutions with a very low concentration of OH^– ions (about 0.1 M). The compound is relatively stable in storage in the dry form, but is strongly hygroscopic. In the structure of I, there are two independent Np(VII) atoms with the oxygen surrounding in the form of tetragonal bipyramids. In contrast to the other salts of the [NpO₄(OH)₂]^3– anions with singlecharged alkali metal cations, the C(NH₂) ₃ ⁺ ions and hydrated Li⁺ ions in I interact with the oxygen surrounding of Np(VII) only via hydrogen bonds of types O_w–H···O and N–H···O with the formation of a three-dimensional H-bond network.     

Kinetics of Thermal Transformation of Mg<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> · 8H<Subscript>2</Subscript>O to Mg<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The kinetics of thermal dehydration of Mg₃(PO₄)₂ · 8H₂O was investigated using thermogravimetry at four different heating rates. The activation energies of the dehydration step of Mg₃(PO₄)₂ · 8H₂O were calculated through the isoconversional Ozawa and Kissinger-Akahira-Sunose (KAS) methods and iterative methods, which were found to be consistent and indicate a single mechanism. The possible conversion function of the dehydration reaction for Mg₃(PO₄)₂ · 8H₂O has been estimated through the Coats and Redfern integral equation, and a better kinetic model such as random nucleation of the “Avrami–Erofeev equation (A _3/2 model)” was found. The thermodynamic functions (ΔH*, ΔG*, and ΔS*) of the dehydration reaction are calculated by the activated complex theory and indicate that it is a non-spontaneous process when the introduction of heat is not connected.     

Crystal Structure of Uranyl Malonate Trihydrate [UO<Subscript>2</Subscript>(OOC)<Subscript>2</Subscript>CH<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)]·2H<Subscript>2</Subscript>O

Single crystals of [UO₂(OOC)₂CH₂(H₂O)]·2H₂O (I) were prepared by recrystallization of finely crystalline uranyl malonate trihydrate under hydrothermal conditions. The crystal structure of I consists of electroneutral [UO₂(OOC)₂CH₂(H₂O)]_n layers and water molecules located between them. The uranium coordination number is 7. The uranium coordination polyhedron is a distorted pentagonal bipyramid with the oxygen atoms of the uranyl group in the apices. The equatorial plane is occupied by four O atoms of three malonate ligands and the water molecule. The malonate anion is coordinated in the bidentate fashion to one uranyl ion to form a six-membered ring and in the monodentate fashion to two other uranyl ions.     

Crystal Structure of a Double Neptunium(V) Lanthanum Nitrate,La(NpO<Subscript>2</Subscript>)<Subscript>3</Subscript>(NO<Subscript>3</Subscript>)<Subscript>6</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O

The structure of a double neptunium(V) lanthanum nitrate, La(NpO₂)₃(NO₃)₆·nH₂O, was studied by single crystal X-ray diffraction. Each neptunyl(V) ion in the structure of the compound is bonded to four other neptunyl(V) ions, acting simultaneously as a bidentate ligand and as a coordination center for two other dioxocations. The cation-cation interaction of the neptunyl(V) ions results in formation of trigonal-hexagonal cationic networks. The surrounding of each Np atom also includes two bidentate nitrate ions. The CN of the Np atom is 8, and the coordination polyhedron is a distorted hexagonal bipyramid. The La³⁺ cations are surrounded only by water molecules.     

Preparation of β-Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>/Poly(D,L-lactide) and β-Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>/Poly(ε-caprolactone) Biocomposite Implants for Bone Substitution

Highly permeable macroporous implants of various architectures for bone grafting have been fabricated by thermal extrusion 3D printing using highly filled β-Ca₃(PO₄)₂/poly(D,L-lactide) (degree of filling up to 70 wt %) and β-Ca₃(PO₄)₂/poly(ε-caprolactone) (degree of filling up to 70 wt %) composite filaments. To modify the surface of the composite macroporous implants with the aim of improving their wettability by saline solutions, we have proposed exposing them to a cathode discharge plasma (2.5 W, air as plasma gas) in combination with subsequent etching in a 0.5 M citric acid solution. It has been shown that the main contribution to changes in the wettability (contact angle) of the composites is made by the changes produced in their surface morphology by etching in a low-temperature plasma and citric acid. An alternative approach to surface modification of the composites is to produce a carbonate hydroxyapatite layer via precipitation from a simulated body fluid solution a factor of 5 supersaturated relative to its natural analog (5xSBF).     

Mechanism of UO<Subscript>2</Subscript>(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O decomposition under the action of microwave radiation

The effect of microwave radiation (MWR) on the decomposition of UO₂(NO₃)₂·6H₂O was studied. Determination of [UO ₂ ²⁺ ] and [NO ₃ ^? ], and also of the molar ratio NO ₃ ^? : UO ₂ ²⁺ in various fractions of the decomposition product showed that the mechanism of the UO₂(NO₃)₂·6H₂O decomposition under the action of MWR differs from the mechanism of its decomposition under common convection heating. The main precursor of UO₃ as product of UO₂(NO₃)₂·6H₂O decomposition under the action of MWR is uranyl hydroxonitrate UO₂(OH)NO₃ formed already in the first minutes of the irradiation. In contrast to the thermolysis under convection heating, UO₂(NO₃)₂ or its hydrates were not detected as intermediates. The mechanism of the UO₂(NO₃)₂·6H₂O decomposition under the action of MWR can be presented by the reactions UO₂(NO₃)₂·6H₂O → UO₂(OH)NO₃ + 5H₂O + HNO₃ and UO₂(OH)NO₃ → UO₃ + HNO₃. The solubility of UO₂(OH)NO₃ in H₂O at 20°C was estimated experimentally at 6.83 × 10^?2 M.     

Synthesis and crystal structure of An(VI) complexes with cyclobutanecarboxylic acid anions and 2,2′-bipyridine [An(VI) = U,Np, Pu]

New complexes of hexavalent U, Np, and Pu of the composition [UO₂(bipy)(cbc)₂] (I) and [AnO₂(bipy)(cbc)₂]·0.5(bipy) [An = Np (II) and Pu (III)] with cyclobutanecarboxylic acid anions C₄H₇COO^– and 2,2′-bipyridine (bipy) were synthesized, and their structures were studied. The An atoms in I–III have the coordination surrounding in the form of distorted hexagonal bipyramids with the О atoms of AnO₂²⁺ cations in the apical positions. The equatorial plane of the bipyramids is constituted by the O atoms of two C₄H₇COO^– anions and N atoms of bipy.     

Mechanism of UO<Subscript>2</Subscript>(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O decomposition under the action of microwave radiation: Part 2

Products of UO₂(NO₃)₂·6H₂O decomposition under the action of microwave radiation (MWR) were studied by thermal gravimetric analysis, X-ray phase analysis, IR spectroscopy, and electron microscopy. The results of physicochemical studies of these decomposition products were compared to the published data for various uranium compounds, including UO₂(NO₃)₂·6H₂O. Apart from gaseous products, the final products of decomposition of 2–10 g of UO₂(NO₃)₂·6H₂O under the action of MWR for 35 min (the maximal process temperature, 170–320°C, is attained in the first 2–5 min of irradiation) are uranyl hydroxonitrate UO₂(OH)NO₃ and uranium trioxide UO₃ or their hydrates. The results obtained are consistent with the mechanism suggested in our previous paper and involving the reactions (1) UO₂(NO₃)₂·6H₂O → UO₂(OH)NO₃ + 5H₂O + HNO₃ and (2) UO₂(OH)NO₃ → UO₃ + HNO_3. The physicochemical study confirms the conclusions on the composition of products of UO₂(NO₃)₂·6H₂O decomposition under the action of MWR, made previously on the basis of chemical studies. The only precursor of UO₃ in microwave treatment of UO₂(NO₃)₂·6H₂O is UO₂(OH)NO₃ (or its hydrates). This is the main difference between the courses of uranyl nitrate decomposition under the conditions of microwave and convection heating. In the latter case, uranyl nitrate and its hydrates also participate in the formation of UO₃.     

Phase relations in the K<Subscript>2</Subscript>MoO<Subscript>4</Subscript>–Ln<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>–Zr(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> (Ln = La–Lu,Y) systems

We have studied phase relations in the K₂MoO₄–Ln₂(MoO₄)₃–Zr(MoO₄)₂ (Ln = La–Lu, Y) systems by the method of “intersecting cuts,” identified pseudobinary joins in their composition triangles, and constructed their phase compatibility diagrams. The systems have been shown to contain new ternary molybdates with the general formula K₅LnZr(MoO₄)₆ (Ln = Dy–Lu and Y). The thermal characteristics of the synthesized compounds have been studied by differential scanning calorimetry in the temperature range 25–700°C. The new ternary molybdates crystallize in a trigonal structure (sp. gr. R\(\bar 3\)c, Z = 6).     

Sol–gel preparation and high-energy XRD study of (CaO)<Subscript>x</Subscript>(TiO<Subscript>2</Subscript>)<Subscript>0.5−x</Subscript>(P<Subscript>2</Subscript>O<Subscript>5</Subscript>)<Subscript>0.5</Subscript> glasses (x = 0 and 0.25)

Glasses from the CaO–TiO₂–P₂O₅ system have potential use in biomedical applications. Here a method for the sol–gel synthesis of the ternary glass (CaO)_0.25(TiO₂)_0.25(P₂O₅)_0.5 has been developed. The structures of the dried gel and heat-treated glass were studied using high-energy X-ray diffraction. The structure of the binary (TiO₂)_0.5(P₂O₅)_0.5 sol–gel was studied for comparison. The results reveal that the heat-treated (CaO)_0.25(TiO₂)_0.25(P₂O₅)_0.5 glass has a structure based on chains and rings of PO₄ tetrahedra, held together by a combination of electrostatic interaction with Ca²⁺ ions and by corner-sharing oxygen atoms with TiO₆ octahedra. In contrast, the (TiO₂)_0.5(P₂O₅)_0.5 glass has a structure based on isolated P₂O₇ units linked together by corner-sharing with TiO₆ groups. The results suggest that both the dried gels possess open porous structures. For the (CaO)_0.25(TiO₂)_0.25(P₂O₅)_0.5 sample there is a significant increase in Ca–O coordination number with heat treatment.     

Synthesis,electronic state,and particle size stabilization of nanoparticulate [Co(OH)<Subscript>2</Subscript>(H<Subscript>3</Subscript>O)<Stack><Subscript>δ</Subscript><Superscript>+</Superscript></Stack>]<Superscript>δ+</Superscript>

We have synthesized nanoparticulate cobalt(II) hydroxide containing Co²⁺ in tetrahedral oxygen coordination (Co _Td ²⁺ ), atypical of such systems: nano- [Co(OH)₂(H₃O) _δ ⁺ ]^δ+. The (Co _Td ²⁺ ) coordination in the hydroxide is inferred from its electronic diffuse reflectance spectrum, which shows a multiplet of strong absorption bands at 14500, 15000, and 16000 cm^?1 (⁴ A ₂(F)-⁴ T ₁(P) transition). Nanoparticulate cobalt(II) hydroxide forms in a weakly acidic medium under essentially nonequilibrium conditions due to supersaturation (by three to four orders of magnitude) with the starting reagents (CoCl₂ and LiOH) at the instant of the formation of the poorly soluble phase Co(OH)₂. Presumably, colloidal particles of nanoparticulate cobalt(II) hydroxide in a weakly acidic aqueous medium have a positive surface charge, compensated by a counter-ion (Cl^?) layer: nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ · δCl^?. The XRD patterns of pastes (gels) containing this hydroxide show three broad-ened lines with d = 5.31 (2θ = 16.7°), 2.77 (2θ = 32.3°), and 2.32 Å (2θ = 38.8°). According to small-angle X-ray scattering data, nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ has a narrow particle size distribution (1.0–2.0 nm). Synthesis and storage conditions are identified which ensure stabilization of the electronic state and particle size of nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ for a long time.     

Theoretical Studies of Electronic Paramagnetic Resonance <Emphasis Type="Italic">g</Emphasis> Factors for La<Subscript>2</Subscript>Mg<Subscript>3</Subscript>(NO<Subscript>3</Subscript>)<Subscript>12</Subscript>⋅24H<Subscript>2</Subscript>O

Lanthanum magnesium double nitrate (LMN) crystals can be used as material for adiabatic demagnetization, magnetic thermometers and a proton spin-polarized target in both physics and polarized neutron diffraction. In the past years, the double nitrates doped with transition metal or rare earth ions have been studied by experimental and theoretical methods. For instance, the electronic paramagnetic resonance (EPR) g factors of the Ce³⁺ ions in La₂Mg₃(NO₃)₁₂⋅24H₂O crystal were measured decades ago. But until now, these useful experimental results have not been theoretically explained. In this work, The EPR g factors of the trigonal Ce³⁺ centers in La₂Mg₃(NO₃)₁₂⋅24H₂O are theoretically studied from the perturbation formulae of the EPR parameters for a 4f¹ ion under the trigonal symmetry crystal field. The used crystal parameters are obtained from the superposition model and the local structure of the studied crystal. The calculated results are reasonably constant to the observed values. The results are discussed.     

Synthesis of M(NpO<Subscript>4</Subscript>)<Subscript>2</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O (M = Mg,Ca, Sr,Ba) Using Н<Subscript>3</Subscript>ВО<Subscript>3</Subscript> Solutions and Properties of These Salts

Two procedures for preparing the compounds M(NpO₄)₂·nH₂O (M = Mg, Ca, Sr, Ba) using boric acid were suggested. In the first procedure, samples of freshly prepared salts M₃(NpO₅)₂·nH₂O (M = Ca, Sr, Ba) are treated with excess 0.5 M H₃BO₃ with vigorous stirring. In the process, the initially light green salts rapidly transform into black products of the general composition M(NpO₄)₂·nH₂O. In the second procedure, a measured volume of a Np(VII) solution with a known LiOH concentration was added to excess 0.5 M H3BO3 solution containing a calculated amount of Mg, Ca, Sr, or Ba nitrate. The reaction yields black precipitates of the same compounds as in the previous case. After washing with water and drying in an oxygen stream, the final products contain a small impurity of Np(VI). The IR spectra suggest that the compounds obtained are structurally related to the previously studied salts MNpO₄ (M = K–Cs), i.e., in their lattices there are neptunium–oxygen layers built of NpO₂³⁺ cations and bridging O atoms. New data on the properties of the compounds M₃(NpO₅)₂·nH₂O with M = Ca, Sr, and Ba were also obtained.     

Morphologies and properties of NiO particles prepared from NiSO<Subscript>4</Subscript>·6H<Subscript>2</Subscript>O and Ni(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O by spray pyrolysis

Nickel oxide particles were prepared by spray pyrolysis of aqueous solutions of NiSO₄·6H₂O and Ni(NO₃)₂·6H₂O. In spray pyrolysis reactor hollow salt particles initially formed were collapsed by decomposition to reduce their size. For NiSO₄·6H₂O less hollowness of the primitive particles and its higher decomposition temperature made the oxide particles highly spherical with very smooth surface. On the other hand the particles prepared from Ni(NO₃)₂·6H₂O were so hollow and fragile with rough surface since they were formed on the liquid pool of the salt melt. The particle size decreased with the furnace set temperature while increased with the initial salt concentration. Single oxide particle was composed of many small nuclei without sintering whose size varied with the rate of decomposition. The crystallinity of the particles increased with both temperature and the initial salt concentration. Preliminary drying in diffusion dryer fixed the size of the oxide particles from NiSO₄·6H₂O at that of the primitive particles, independent of the temperature. However, by the preliminary drying the particles from Ni(NO₃)₂·6H₂O became more hollow and fragile, whose sizes decreased with the temperature.