Chemistry of the CARBEX process: Identification of absorption bands of the ligands in the electronic spectra of aqueous solutions of Na<Subscript>4</Subscript>[UO<Subscript>2</Subscript>(CO<Subscript>3</Subscript>)<Subscript>3</Subscript>]

On the basis of consideration of hydration, hydrolysis, dissociation, polymerization, and ligand exchange that occur in aqueous solutions of U(VI) complexes, a new approach to the assignment of absorption bands of the ligands in electronic spectra of uranium(VI) carbonate complexes in the range 190–400 nm has been suggested. For the Na₄[UO₂(CO₃)₃] complex, the following assignment of absorption bands has been made: Na₃[UO₂(CO₃)₃]^–, 258 nm; Na₂[UO₂(CO₃)₃]^2–, 300 nm; and Na₄[UO₂(CO₃)₃], 330 nm.     

Crystal and molecular structure of ammonium trinitratouranylate NH<Subscript>4</Subscript>[UO<Subscript>2</Subscript>(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>]

Ammonium trinitratouranylate NH₄[UO₂(NO₃)₃] (I) single crystals have been synthesized by the reaction of aqueous solutions of diaquadinitratouranyl tetrahydrate and ammonium nitrate in the presence of nitric acid. The structure of the complex has been studied by X-ray diffraction analysis: space group \(R\bar 3c\), a = 9.361(2), c = 18.883(4) Å; V = 1433.0(5) ų, and Z = 6. The structural units of the NH₄[UO₂(NO₃)₃] crystal—NH ₄ ⁺ cations and [UO₂(NO₃)₃]^? complex anions with three bidentate cyclic nitrato groups—are on crystallographic axes \(\bar 3\). A complex three-dimensional packing arranged by the electrostatic attraction forces between counterions and the N-H...O hydrogen bonds between ammonium cations and trinitratouranylate anions is realized in the structure. X-ray diffraction analysis results are confirmed by IR spectra of NH₄[UO₂(NO₃)₃].     

Synthesis and structure of [UO<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>){CONH<Subscript>2</Subscript>N(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>}<Subscript>2</Subscript>]

The single crystals of [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] were synthesized and studied by X-ray diffraction. The crystals are monoclinic, a = 7.461(2) Å, b = 8.828(2) Å, c = 11.756(2) Å, β = 107.21(3)°, space group Pc, Z = 2, R = 2.94%. The structure comprises infinite chains [UO₂(C₂O₄){CONH₂N(CH₃)₂}₂] extended along [001] and corresponding to the AT¹¹M ₂ ¹ crystallochemical group (A = UO ₂ ²⁺ , T¹¹ = C₂O ₄ ^2? , M¹ = N,N-CONH₂N(CH₃)₂) of uranyl complexes. The chains are connected into a three-dimensional framework by hydrogen bonds involving the oxygen atoms of oxalate and uranyl ions and the N,N-dimethylcarbamide methyl groups.     

Chemistry of the CARBEX process. Identification of the absorption bands of the ligands in the electronic spectra of U(VI) extracts with methyltrioctylammonium carbonate

The electronic absorption bands of extracts of the Na₄[UO₂(O₂)(CO₃)₂] complex with methyltrioctylammonium (MTOA) carbonate were assigned taking into account hydration, hydrolysis, dissociation, polymerization, and ligand exchange, which occur in aqueous and organic solutions. It was shown that the extractable compound, (R₄N)₄[UO₂(O₂)(CO₃)₂], present in low concentrations in the organic phase partly dissociates by one step to give the (R₄N)₃[UO₂(O₂)(CO₃)₂]^– anions, while at high concentrations, it is converted to polynuclear complex.     

Synthesis and crystal structure of (NH<Subscript>4</Subscript>)(CN<Subscript>3</Subscript>H<Subscript>6</Subscript>)[UO<Subscript>2</Subscript>(SeO<Subscript>3</Subscript>)<Subscript>2</Subscript>]

Single crystals of (NH₄)(CN₃H₆)[UO₂(SeO₃)₂] (I) are synthesized and studied by X-ray diffraction analysis. The compound crystallizes in the triclinic crystal system with the unit cell parameters: a = 7.0051(2) Å, b = 9.4234(3) Å, c = 9.5408(3) Å, α = 88.727(1)°, β = 70.565(1)°, γ= 77.034(1)°, space group P ₁, Z = 2, R = 0.0224. The main structural units of crystals I are the [UO₂(SeO₃)₂]^2? chains of the crystal-chemical group AB²B₁₁ (A = UO ₂ ²⁺ , B₂= SeO₃ ^2?, B₁₁= SeO₃ ^2?) of the uranyl complexes. The uranium-containing complexes are joined into a three-dimensional framework by the ammonium and guanidinium ions and a system of hydrogen bonds.     

Structure and some properties of [UO<Subscript>2</Subscript>(SeO<Subscript>4</Subscript>)(C<Subscript>5</Subscript>H<Subscript>12</Subscript>N<Subscript>2</Subscript>O)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)]

The complex [UO₂(SeO₄)(C₅H₁₂N₂O)₂(H₂O)] (I) was synthesized and studied by thermal analysis, IR spectroscopy, and X-ray crystallography. The crystals are orthorhombic: a = 13.1661(3) Å, b = 16.4420(5) Å, c = 17.4548(6) Å, Pbca, Z = 8, R = 0.0423. The structural units of crystal I are chains with the composition coinciding with that of the compounds of the AB₂M ₃ ¹ crystal chemical group of the uranyl complexes (A = UO ₂ ²⁺ , B² = SeO ₄ ^2? , M¹ = C₅H₁₂N₂O and H₂O).     

Crystal Structure of [UO<Subscript>2</Subscript>SO<Subscript>4</Subscript>{(CH<Subscript>3</Subscript>)HNCONH(CH<Subscript>3</Subscript>)}<Subscript>2</Subscript>]

The single crystals of [UO₂SO₄{(CH₃)HNCONH(CH₃)}₂] (I) were synthesized and studied by X-ray diffraction. The crystals are monoclinic, a = 6.847(1) Å, b = 14.259(3) Å, c = 14.297(3) Å, β = 93.451(4)°, space group P2₁/n, Z = 4. The main structural units of crystals I are ribbons whose composition coincides with the composition of the compound. The crystal chemical formula of the complex is AT³M ₂ ¹ (A = UO ₂ ²⁺ ).     

Crystal structure of [CuL](NO<Subscript>3</Subscript>)(ReO<Subscript>4</Subscript>) and [CuL](ReO<Subscript>4</Subscript>)<Subscript>2</Subscript> (L = 4,6,6-trimethyl-1,9-diamino-3,7-diazanon-3-en)

The crystal structures of [CuL](NO₃)(ReO₄) and [CuL](ReO₄)₂ (L is 4,6,6-trimethyl-1,9-diamino-3,7-diazanon-3-en) are studied. The square coordination of the copper atom in [CuL](NO₃)(ReO₄) is completed to a distorted octahedron by two oxygen atoms: Cu…O (ReO ₄ ^? ) 2.393 Å and Cu…O (NO ₃ ^? ) 2.685 Å, and that in [CuL](ReO₄)₂, by Cu…O(ReO ₄ ^? ) 2.468 Å and 2.697 Å. The products of thermolysis of the salts in a hydrogen atmosphere at 800°C are mixtures of nanocrystalline metal powders with coherent scattering regions of ～45 nm.     

Structure and some properties of [UO<Subscript>2</Subscript>CrO<Subscript>4</Subscript>{CH<Subscript>3</Subscript>CON(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>}<Subscript>2</Subscript>]

A new complex [UO₂CrO₄{CH₃CON(CH₃)₂}₂] (I) was studied by thermal analysis, IR spectroscopy, and X-ray crystallography. The crystals are monoclinic: a = 13.8108(11) Å, b = 8.6804(7) Å, c = 13.0989(10) Å, β = 104.777(1)°, V = 1518.4(2) ų, space group P2₁/c, Z = 4, R = 2.39%. The structure of I contains infinite chains of the [UO₂CrO₄{CH₃CON(CH₃)₂}₂] composition running along [001]; the complex belongs to the AT¹¹M¹ ₂ crystal-chemical group (A = UO ₂ ²⁺ , T¹¹ = CrO ₄ ^2? , M¹ = CH₃CON(CH₃)₂) of uranyl complexes. The chains are linked into a three-dimensional framework due to hydrogen bonds between oxygen atoms of chromate ions and hydrogen atoms of methyl groups of the dimethylacetamide.     

Crystal structure of [Bi(<Emphasis Type="Italic">N</Emphasis>-ethylthiourea)<Subscript>4</Subscript>(ClO<Subscript>4</Subscript>)<Subscript>2</Subscript>]ClO<Subscript>4</Subscript>

The structure of the bismuth(III) complex with N-ethylthiourea (Ettu) has been determined for the first time. We found that the crystal structure of [Bi(Ettu)₄(ClO₄)₂]ClO₄ is built of distorted octahedral cations [Bi(Ettu–S)₄(ClO₄)₂]ClO₄]⁺ and anions ClO₄^-. The deviation of one of the two independent Ettu molecules from the plane structure is explained by the mutual repulsion of the ligands and the formation features of hydrogen bonds. The C₂H₅(Ettu) group is in the cis position relative to the thiocarbonyl group.     

The thermodynamic characteristics of vaporization in the NaI-PrI<Subscript>3</Subscript> system

The vaporization of the NaI-PrI₃ quasi-binary system was studied by high-temperature mass spectrometry over the whole concentration range. At 623–994 K, saturated vapor contained not only (NaI) _n and (PrI₃) _n molecules (n = 1, 2) and Na⁺(NaI) _n (n = 0–4) and I^?(PrI₃) _n (n = 1–2) ions but also mixed molecular and ionic associates recorded for the first time (NaPrI₄, Na₂PrI₅, NaPrI ₃ ⁺ , Na₂PrI ₄ ⁺ , Na₃PrI ₅ ⁺ , Na₄PrI ₆ ⁺ , NaPrI ₅ ^? , and NaPr₂I ₈ ^? ). The partial vapor pressures of molecules were calculated, and the equilibrium constants of the dissociation of neutral and charged associates were measured. The enthalpies of molecular and ion-molecular reactions were determined, and the enthalpies of formation of gaseous molecules and ions were obtained.     

Synthesis and Properties of Double Complex Salts Containing the Cation [Co(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>]<Superscript>3+</Superscript>

A series of complexes [Co(NH₃)₆] _x [ML₆₍₄₎] _y , where M is Fe(III) and Fe(II), Cr(III), Cu(II); L is CN^?, NCS^?, 1/2C₂O ₄ ^2? , are synthesized. Their IR spectra and thermal decomposition in air are studied, and interplanar distances in crystalline lattices of the complexes are determined. The compounds can be used as precursors for producing homogeneous bimetallic nanodimensional powders.     

Phase transitions in double molybdates K<Subscript>2</Subscript>M<Stack><Subscript>2</Subscript><Superscript>II</Superscript></Stack>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> with M = Mg or Co

Phase transitions and cation mobility in double molybdates K₂M ₂ ^II (MoO₄)₃ with M = Mg or Co and the products of their heterovalent doping with scandium(III) and vanadium(V) have been studied. The transition from low to high conductivity in K₂M ₂ ^II (MoO₄)₃ is the result of a two-stage phase transition, whose occurrence is significantly extended in time. Heterovalent substitutions noticeably decrease the heat of the phase transition. The transition to the low-temperature phase is not achieved even after long-term exposure.     

The thermodynamic properties of the [(Me<Subscript>3</Subscript>Si)<Subscript>7</Subscript>C<Subscript>60</Subscript>]<Subscript>2</Subscript> fullerene complex

The temperature dependence of the heat capacity C _p ^o of the [(Me₃Si)₇C₆₀]₂ fullerene complex was measured for the first time using precision adiabatic vacuum calorimetry over the temperature range 6.7–340 K and high-accuracy differential scanning calorimetry at 320–635 K. For the most part, the error in the C _p ^o values was about ±0.5%. An irreversible endothermic effect caused by the splitting of the dimeric bond between fullerene fragments and the thermal decomposition of the complex was observed at 448–570 K. The thermodynamic characteristics of this transformation were calculated and analyzed. Multifractal analysis of the low-temperature (T < 50 K) heat capacity was performed, and conclusions were drawn concerning the character of the heterodynamicity of the structure. The experimental data obtained were used to calculate the standard thermodynamic functions C _p ^o (T), H ^o (T) ? H ^o (0), S ^o (T) ? S ^o (0), and G ^o (T) ? H ^o (0) over the temperature range from T → 0 to 445 K and estimate the standard entropy of formation of the compound from simple substances at 298.15 K. The standard thermodynamic properties of [(Me₃Si)₇C₆₀]₂ are compared with those of the (C₆₀)₂ dimer, the [(η⁶-Ph₂)₂Cr]⁺[C₆₀]^?? fulleride, and the initial C₆₀ fullerene.     

Be<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>CO<Subscript>3</Subscript> solubility in carbonate and fluoride aqueous solutions

Be₂(OH)₂CO₃ solubilities at 25°C in 0.7 M NaClO₄ solutions containing variable NaHCO₃ and Na₂CO₃ concentrations has been experimentally determined. The solubilities increase with increasing carbonate alkalinity. The results of the experiments do not contradict the suggestion that the mixed hydroxocarbonate complex Be₂(OH)₂CO ₃ ^2? is the major beryllium solute species. At fluoride concentrations higher than 250 μmol/L, the Be₂(OH)₂CO₃ solubilities noticeably increase as a result of the formation of beryllium fluoride complexes.     

Thermal properties,phase transitions,vibrational and reorientational dynamics of [Mn(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

[Mn(NH₃)₆](NO₃)₂ crystallizes in the cubic, fluorite (C1) type crystal lattice structure (Fm \( \overline{3} \) m) with a = 11.0056 Å and Z = 4. Two phase transitions of the first-order type were detected. The first registered on DSC curves as a large anomaly at T _C1 ^h  = 207.8 K and T _C1 ^c  = 207.2 K, and the second registered as a smaller anomaly at T _C2 ^h  = 184.4 K and T _C2 ^c  = 160.8 K (where the upper indexes h and c denote heating and cooling of the sample, respectively). The temperature dependence of the full width at half maximum of the band associated with the δ_s(HNH)F_1u mode suggests that the NH₃ ligands in the high temperature and intermediate phase reorientate quickly with correlation times in the order of several picoseconds and with activation energy of 9.9 kJ mol^?1. In the phase transition at T _C2 ^c probably only a some of the NH₃ ligands stop their reorientation, while the remainders continue to reorientate quickly with activation energy of 7.7 kJ mol^?1. Thermal decomposition of the investigated compound starts at 305 K and continues up to 525 K in four main stages (I–IV). In stage I, ²/₆ of all NH₃ ligands were seceded. Stages II and III are connected with an abruption of the next ²/₆ and ¹/₆ of total NH₃, respectively, and [Mn(NH₃)](NO₃)₂ is formed. The last molecule of NH₃ per formula unit is freed at stage IV together with the simultaneous thermal decomposition of the resulting Mn(NO₃)₂ leading to the formation of gaseous products (O₂, H₂O, N₂ and nitrogen oxides) and solid MnO₂.     

Low-temperature heat capacity of sodium erbium molybdophosphate Na<Subscript>2</Subscript>Er(MoO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)

Adiabatic calorimetry is used to measure the low-temperature heat capacity of Na₂Er(MoO₄)(PO₄)from 6.41 to 347.87 K. Experimental data are used to calculate the thermodynamic functions of Na₂Er(MoO₄)(PO₄), which at 298.15 K are as follows: C _p ⁰ (298.15 K) = 243,3 ± 0.4 J/(K mol), S ⁰(298.15 K) = 312.8 ± 0.8 J/(K mol), H ⁰(298.15 K) ? H ⁰(0 K) = 45280 ± 90 J/mol, and Φ⁰(298.15 K) = 136.1 ± 0.3 J/(K mol). A diffuse heat-capacity anomaly associated with splitting of the Stark levels (Schottky anomaly) is discovered in the low-temperature region.     

Low-temperature heat capacity and high-temperature thermal behavior of sodium lutetium molybdate phosphate Na<Subscript>2</Subscript>Lu(MoO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)

The low-temperature heat capacity of Na₂Lu (MoO₄)(PO₄) was measured by adiabatic calorimetry in the range of 7.47–345.74 K. The experimental data were used to calculate the thermodynamic functions of Na₂Lu (MoO₄)(PO₄). At 298.15 K, the following values were obtained: C _p ⁰ (298.15 K) = 237.7 ± 0.1 J/(K mol), S ⁰(298.15 K) = 278.1 ± 0.8 J/(K mol), H ⁰(298.15 K) ? H ⁰ (0 K) = 42330 ± 20 J/mol, and Φ⁰(298.15 K) = 136.1 ± 0. 3 J/(K mol). A heat capacity anomaly was found in the range of 10-67 K with a maximum at T _tr = 39.18 K. The entropy and enthalpy of transition are ΔS = 12.39 ± 0.75 J/(K mol) and ΔH = 403 ± 16 J/mol. The thermal investigation of sodium lutetium molybdate phosphate in the high-temperature range (623–1223 K) was performed using differential scanning calorimetry. It was found that during melting in the range of 1030–1200 K, Na₂Lu(MoO₄)(PO₄) degrades to simpler compounds; the degradation scenario is verified by X-ray powder diffraction.     

Synthesis of dugganite Pb<Subscript>3</Subscript>TeZn<Subscript>3</Subscript>As<Subscript>2</Subscript>O<Subscript>14</Subscript> and its analogues

A ₃ ²⁺ Te⁶⁺M ₃ ²⁺ X ₂ ⁵⁺ O₁₄ (A = Pb, Ba, Sr; M = Zn, Mg, Co, Mn, Cu, Cd; X = P, As, V) compounds and Pb₃WZn₃P₂O₁₄, all with Ca₃Ga₂Ge₄O₁₄ structure (space group P321), were prepared by solid-phase synthesis in air at 600–1000°C. Most compounds melt incongruently or experience solid-phase decomposition.     

The first chromate containing both Cr<Subscript>2</Subscript>O<Subscript>7</Subscript> and Cr<Subscript>3</Subscript>O<Subscript>10</Subscript> groups,bis(1,3-bis(4-piperidinium)propane) dichromate trichromate monohydrate: Synthesis and crystal structure

A new organic-inorganic hybrid material (C₁₃H₂₈N₂)₂[Cr₂O₇][Cr₃O₁₀]·H₂O (1) was synthesized by slow solvent evaporation at room temperature, and its crystal structure was determined by single crystal X-ray diffraction. This compound crystallizes in the monoclinic space group P2₁/c. The asymmetric unit contains two crystallographically independent 1,3-bis(4-piperidinium)propane, (H₂bppp)²⁺ cations (A and B), one trichromate Cr₃O ₁₀ ^2? anion, one dichromate Cr₂O ₇ ^2? anion, and one water molecule. All these entities are interconnected into a complicated two-dimensional hydrogen bonded network via N–H?O and O–H?O hydrogen bonds. Furthermore, this structure is stabilized by a large number of C–H?O interactions, thus establishing a three-dimensional network structure. This compound appears to be the first example of chromates containing both Cr₂O₇ and Cr₃O₁₀ groups.