Equilibria of aqueous solutions of isopolyniobotungstates-6 with c Nb : c W = 1 : 5

Complex formation in the Nb₆O ₁₉ ^8? -WO ₄ ^2? -H⁺-H₂O system with c _Nb : c _W = 1 : 5 and varied c _{Nb + W} ⁰ = 10^?2, 5 × 10^?3, 2.5 × 10^?3, and 10^?3 mol/L) has been studied. Distribution diagrams were simulated for individual niobium(V) and tungsten(VI) isopolyanions and mixed isopolyniobotungstates for $Z = \frac{{c_{H^ + }^0 }}{{c_{Nb + W}^0 }} = 0 - 3.0$ in an NaCl background electrolyte. We have shown that isopolyniobotungstates-6 of composition H _x NbW₅O ₁₉ ^{(3 ? x)?} are formed via H _x Nb _n W_6?n O ₁₉ ^{(2 + n ? x)?} (n=2, 3, 5) ions. The concentration formation constants and thermodynamic formation constants of isopolyniobotungstate anions (IPNTAs) in aqueous solution have been calculated. Salt Tl₃NbW₅O₁₉·9H₂O has been synthesized and identified by chemical analysis and IR spectroscopy.     

Sampling of aryldiazonium, anilino, and aryl radicals by membrane introduction mass spectrometry: Thermolysis of aromatic diazoamino compounds

Membrane introduction mass spectrometry (MIMS) is used to sample free radicals generated by thermolysis at atmospheric pressure. This is done by heating the solid sample in a custom-made probe that is fitted with a silicone membrane to allow selective and rapid introduction of the pyrolysates into the ion source of a triple quadrupole mass spectrometer. Phenyldiazonium radical (C₆H₅N ₂ ^· ) and some of its ring-substituted analogs, the methoxy anilino radical CH₃OC₆H₄NH^·, and aryl radicals are generated by gas phase thermolysis of symmetrical aryl diazoamino compounds (ArNH-N₂Ar). The radicals are identified by measurement of their ionization energies (IE) using threshold ionization efficiency data. A linear correlation between the ionization energy of the phenyldiazonium radicals and their Brown σ⁺ values is observed, and this confirms the formation of these species and validates the applicability of MIMS in sampling these radicals. The ionization energies of the aryldiazonium radicals are estimated as IE (p-CH₃O-C₆H₄N ₂ ^· ), 6.74 ± 0.2 eV; IE (p-CH₃-C₆H₄N ₂ ^· ), 7.72 ± 0.2 eV; IE (C₆H₅N ₂ ^· ), 7.89 ± 0.2 eV; IE (m-Cl-C₆H₄N ₂ ^· ), 7.91 ± 0.2 eV; IE (p-F-C₆H ₄ ^· N ₂ ^· ), 8.03 ± 0.2 eV; and IE (m-NO₂-C₆H₄N ₂ ^· ), 8.90 = 0.2 eV. The ionization energies of the aryl radicals are estimated as IE (p-CH₃O-C₆H ₄ ^· ), 7.33 ± 0.2 eV; IE (p-CH₃-C₆H ₄ ^· ), 8.31 ± 0.2 eV; IE (C₆H ₅ ^· ), 8.44 ± 0.2 eV; IE (m-Cl-C₆H ₄ ^· ), 8.50 ± 0.2 eV and IE (p-F-C₆H ₄ ^· ), 8.54 ± 0.2 eV. Also, the ionization energy of the p-methoxyanilino radical (p-CH₃O-C₆H₄NH^·) is estimated as 7.63 ± 0.2 eV.     

Study of new molecular and crystal structures of 4,4,10,10-tetramethyl-1,3,7,9-tetraazospiro[5.5]undecane-2,8-dione and its salts: Monochloride,mononitrate, and tetraiodotellurate

This is the first work to synthesize 4,4,10,10-tetramethyl-1,3,7,9-tetraazospiro[5.5]undecane-2,8-dione monohydrate, monochloride, mononitrate, and teteraiodotellurate: C₁₁H₂₀N₄O₂·H₂O (I), C₁₁H₂₁N₄O ₂ ⁺ ·Cl^? (II), C₁₁H₂₁N₄O ₂ ⁺ ·NO ₃ ^? (III), and 2(C₁₁H₂₁N₄O ₂ ⁺ )·TeI ₄ ^2? ·C₃H₆O (IV) and determine their structures. Crystals of I are monoclinic: space group P2₁/c, at 298 K a = 5.7118(7) Å, b = 17.842(2) Å, and c = 13.5905(16) Å; β = 91.621(11)°; V = 1384.5(3) ų; d _x = 1.239 g/cm³, Z = 4. Crystals of II are tetragonal: space group P4₃, at 298 K a = 6.4134(3) Å and c = 34.292(2) Å; V = 1410.47(14) ų; d _x = 1.303 g/cm³; Z = 4. Crystals of III are triclinic: space group \(P\bar 1\) , at 298 K a = 8.7614(14) Å, b = 9.3904(18) Å, and c = 10.028(2) Å; α = 63.27(2)°, β = 78.591(16)°, and γ = 84.308(15)°; V = 722.3(2) ų; d _x = 1.40 g/cm³; Z = 2. Crystals of IV are triclinic: space group \(P\bar 1\) , at 100 K a = 10.4630(4) Å, b = 11.9372(6) Å, and c = 16.4118(5) Å; α = 72.058(3)°, β = 76.406(3)°, and γ = 87.029(3)°; V = 1895.04(12) ų; d _x = 2.06 g/cm³; Z = 2. The synthesis of s and p metals with spirocarbone in acetone medium is found to be impossible due to the protonation by the oxygen atom of the carbonyl group. The main crystalline product of the complexation reaction is a monosalt. Evidence is provided that the recrystallization and drying of the synthesized spirocarbone preparation yields monohydrate (I); its purity and monophasity is confirmed by a Rietveld refinement of the powder X-ray pattern. The lattice parameters at room temperature are: a = 5.6885(12) Å, b = 17.8496(12) Å, and c = 13.518(3) Å; β = 91.449(15)°; V = 1372.1(4) ų. The sample is monophasic.     

Synthesis and crystal structure of dibenzo-18-crown-6 oxonium perchlorate trihydrate

A hydrated crystalline ionized adduct of dibenzo-18-crown-6 and perchloric acid DB18C6 · H₃O⁺ · CiO ₄ ^? · 3H₂O (I) is synthesized and characterized by X-ray diffraction. The crystals of I are monoclinic: a = 17.760 Å, b = 12.922 Å, β = 124.27°, Z = 4, space group Cc. The structure of I is solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.079 for 3294 independent reflections (CAD4 automated diffractometer, λMoK _α radiation). A DB18C6 molecule has a butterfly conformation with the rough symmetry C _2v . An H₃O⁺ · H₂O dimer is situated on one side of the DB18C6 macrocycle, and the ClO ₄ ^? anion and two other water molecules are on the other side. In the crystal of I, the DB18C6 molecules, H₃O⁺ and ClO ₄ ^? ions, and water molecules are linked through intermolecular (interionic) hydrogen bonds to form broad infinite chains running along the z axis.     

Pressure and isotope effects on the proton jump of the hydroxide ion at 25°C

The limiting molar conductances Λ⁰ of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 25°C as a function of pressure to disclose the difference in the proton-jump mechanism between an OH^? (OD^?) and a H₃O⁺ (D₃O⁺) ion. The excess conductance of the OD^? ion in D₂O λ _E ^O (OD ^-), as estimated by the equation $$\lambda _E^O (OD^ - ) = \Lambda ^O (KOD/D_2 O) - \Lambda ^O (KCl/D_2 O)$$ increases a little with pressure as well as the excess conductance of the OH^? ion in H₂O $$\lambda _E^O (OH^ - ) = \Lambda ^O (KOH/H_2 O) - \Lambda ^O (KCl/H_2 O)$$ However, their rates of increase with pressure are much smaller than those of the excess deuteron and proton conductances, λ _E ^O (D ⁺) and λ _E ^O (H ⁺). With respect to the isotope effect on the excess conductance, λ _E ^O (OH ^-)/λ _E ^O (D ⁺) decreases with presure as in the case of λ _E ^O (H ⁺)/λ _E ^O (D ⁺), but the value of λ _E ^O (OH ^-)/λ _E ^O (OD ^-) itself is much larger than that of λ _E ^O (H ⁺)/λ _E ^O (D ⁺) at each pressure. These results are ascribed to the difference in the pre-rotation of water molecules, which is brought about by the difference in the intial orientation of the rotating water molecule adjacent to the OH^? (OD^?) or the H₃O⁺ (D₃O⁺) ion.     

Crystal structure of two hydrate phases of ciprofloxacindi-um tetrachloridocobaltate(II)

New (C₁₇H₂₀FN₃O₃)₂[CoCl₄]₂·3H₂O (I) and C₁₇H₂₀FN₃O₃[CoCl₄]·H₂O (II) compounds, where C₁₇H₁₈FN₃O₃ is ciprofloxacin (CfH), are synthesized and their crystal structures are determined. Crystallographic data for I: a = 18.441(5) Å, b = 9.030(3) Å, c = 27.551(8) Å, V = 4588(4) ų, space group Pca2₁, Z = 4; for II: a = 9.305(3) Å, b = 9.885(3) Å, c = 12.999(4) Å, α = 82.782(4)°, β = 72.954(4)°, γ = 89.736(4)°, V = 1133(1) ų, P-1 space group, Z = 2. Both structures contain CfH ₃ ²⁺ ion pairs bonded by the π-π interaction. Additionally, in the crystal of I there is a stacking interaction between the π clouds of aromatic rings and hydrogen atoms of the cyclopropyl group linking the pairs of molecules with each other. The structure of the centrosymmetric crystal of triclinic phase II is also formed from CfH ₃ ²⁺ ion pairs bonded by the π-π interaction, which, in this case, are not independent because they are related by the symmetry center. Hydrogen bonds form a branched three-dimensional network linking the CfH ₃ ²⁺ and CoCl ₄ ^2? ions and water molecules.     

3-(diallylamino)propanenitrile ((C3H5)2NC2H4CN, L) π-complexes with copper(I) ionic salts. Syntheses and crystal structures of compounds [Cu(H+L)ClO4]ClO4 · H2O, [Cu(H+L)BF4]BF4 · H2O, and [Cu(H+L)(H2O)]SiF6 · H2O

Qualitative single crystals of ??-complexes Cu(H⁺L)(ClO₄)]ClO₄ · H₂O (I), Cu(H⁺L)(BF₄)]BF₄ · H₂O (II), and [Cu(H⁺L)(H₂O)]SiF₆ · H₂O (III) are synthesized from solutions of 3-(diallylamino)propanenitrile (L) in propanol, ethanol, and methanol-water acidified with the corresponding acid to pH 3.5?C5 and from the copper(II) salts (Cu(ClO₄)₂ · 6H₂O, Cu(BF₄)₂ · 6H₂O, and CuSiF₆ · 4H₂O) using the alternating-current electrochemical method on copper wire electrodes. The crystal structures of the complexes are determined. All compounds crystallize in the monoclinic crystal system: complexes I and II are isostructural, space group P2₁/n, Z = 4. For compound III, space group P2₁/c, Z = 8. Unit cell parameters: for I a =7.8153(3), b = 16.7824(7), c = 12.4426(5) ?, ?? = 93.410(2)°, V = 1629.1(1) ?³; for II, a = 7.6755(4), b = 16.7119(7), c = 12.3784(6) ?, ?? = 94.354(2)°, V = 1583.2(1); and for III a = 9.826(2), b = 24.009(3), c = 12.061(2) ?, ?? = 91.820(6)°, V = 2843.9(7) ?³. The trigonal pyramidal coordination of the copper atom in complexes I-III is formed by two C=C bonds of the allyl groups of H⁺L, the nitrile N atom of the adjacent cation of the ligand, and the O or F atom of the ClO ₄ ^? or BF ₄ ^? anions. In structure III, the apical position of the pyramid is occupied by the O atom of the water molecule, since the SiF ₆ ^2? anion is considerably remote from the copper(I) atom. However, this anion is bound to the organic cation by hydrogen bonds F??H (2.05?C2.51 ?).     

Thermochemical charge generation in polymer-salt films as a function of temperature

Potential was studied as a function of temperature during charge generation in poly(vinyl alcohol) films containing ammonium heptamolybdate, copper nitrate, and polyoxometalate (NH₄)₄₂[Mo ₇₂ ^VI Mo ₆₀ ^V O₃₇₂(HCOO)₃₀(H₂O)₇₂] · 30HCOONH₄ · 250H₂O. The range of the strongest charge generation and its bounds were determined. The results are matched to thermal analysis data. Charge generation correlates with evolution of volatiles from the films.     

Syntheses, structural characterization, and antibacterial properties of a hexanuclear bimetallic cluster complex

A new bimetallic cluster complex with the formular {[Cu(Phen)₂]₂V₄O₁₂} · MeOH · 5H₂O has been synthesized and structurally characterized by elemental analyses, IR spectrum, and single crystal X-ray diffraction. The heterobimetallic cluster complex is composed of a discrete V₄O ₁₂ ^4? cluster covalently attached to two [Cu(Phen)₂] ₂ ²⁺ fragments. The nonclassical hydrogen bonds and π-π stacking contribute to the formation of the three-dimensional supramolecular structure. Microdilution broth method indicated that the complex showed significant activity against B. subtilis, S. aureus, and E. coli.     

Photosensitized formation of peroxyl radicals in aqueous solutions of adenine at 77 K

Conditions for the formation of peroxyl radicals photosensitized by near-UV irradiation in frozen aqueous solutions of adenine containing 0.1 M NaCl (pH 4–7) are studied. Analysis of the EPR spectra shows that the systems under study contain two types of peroxyl radicals presumably classified earlier as O ₂ ^?· and HO _2· ^· . The effect of freezing methods on the production of the radicals is shown. The signal from O ₂ ^?· predominates in the spectra of samples with open surfaces and is likely due to the reduction of adsorbed O₂ molecules with photoejected electrons. The signal from HO ₂ ^· could be due to photoinduced interaction between the sensitizer and solvent. Possible mechanisms of these processes are considered.     

Thermochemical study of [Sm(C7H5O3)2·(C4H6NO2S)]·2H2O

The product from reaction of samarium chloride hexahydrate with salicylic acid and Thioproline, [Sm(C₇H₅O₃)₂·(C₄H₆NO₂S)]·2H₂O, was synthesized and characterized by IR, elemental analysis, molar conductance, and thermogravimetric analysis. The standard molar enthalpies of solution of [SmCl₃·6H₂O(s)], [2C₇H₆O₃(s)], [C₄H₇NO₂S(s)] and [Sm(C₇H₅O₃)₂·(C₄H₇NO₂S)·H₂O(s)] in a mixed solvent of absolute ethyl alcohol, dimethyl sulfoxide(DMSO) and 3 mol L^?1 HCl were determined by calorimetry to be Δ_s H _m ^Φ [SmCl₃ δ6H₂O (s), 298.15 K]= ?46.68±0.15 kJ mol^?1 Δ_s H _m ^Φ [2C₇H₆O₃ (s), 298.15 K]= 25.19±0.02 kJ mol^?1, Δ_s H _m ^Φ [C₄H₇NO₂S (s), 298.15 K]=16.20±0.17 kJ mol^?1 and Δ_s H _m ^Φ [Sm(C₇H₅O₃)₂·(C₄H₆NO₂S)]·2H₂O (s), 298.15 K]= ?81.24±0.67 kJ mol^?1. The enthalpy change of the reaction (1) $$ SmCl_3 \cdot 6H_2 O(s) + 2C_7 H_6 O_3 (s) + C_4 H_7 NO_2 S(s) = Sm(C_7 H_5 O_3 )_2 \cdot (C_4 H_6 NO_2 S) \cdot 2H_2 O(s) + 3HCl(g) + 4H_2 O(1) $$ was determined to be Δ_s H _m ^Φ =123.45±0.71 kJ mol^?1. From date in the literature, through Hess’ law, the standard molar enthalpy of formation of Sm(C₇H₅O₃)₂(C₄H₆NO₂S)δ2H₂O(s) was estimated to be Δ_s H _m ^Φ [Sm(C₇H₅O₃)₂·(C₄H₆NO₂S)]·2H₂O(s), 298.15 K]= ?2912.03±3.10 kJ mol^?1.     

Luminescent zinc(II) and cadmium(II) complexes based on 2-(4,5-dimethyl-1H-imidazol-2-yl)pyridine and 2-(1-hydroxy-4,5-dimethyl-1H-imidazol-2-yl)pyridine

Complexes ZnL¹Cl₂, CdL¹Cl₂, ZnL ₂ ¹ Cl₂ ^·1.5H₂O, CdL ₂ ¹ Cl₂ ^·2H₂O, CdL ₂ ¹ Cl₂ ^·MeOH·H₂O [L¹ = 2-(4,5-dimethyl-1H-imidazol-2-yl)pyridine] and inner-complex compounds ZnL ₂ ² ·2H₂O, CdL ₂ ² [HL² = 2-(1-hydroxy-4,5-dimethyl-1H-imidazol-2-yl)pyridine] were synthesized. The complexes exhibit bright photoluminescence in the blue region of the spectrum, with the intensity exceeding this characteristic of the compounds L¹ and HL². Compound L¹ in aqueous solution is a potential chemosensor for the determination of zinc and cadmium.     

Synthesis of bismuth complexes from bismuth iodide and ammonium and phosphonium salts

The complexes [Et₂NH₂] ₃ ⁺ [BiCl₆]^3? (I), [NH₄]⁺[BiI₄(C₅H₅N)₂]^?·2C₅H₅N (II), [Ph₃MeP] ₂ ⁺ [BiI₅]^2? (III), [Ph₃MeP] ₂ ⁺ [BiI₅(C₅H₅N)]^2?·C₅H₅N (IV), [Ph₃MeP] ₃ ⁺ [Bi₃I₁₂]^3? (V), [Ph₃(i-Pr)P] ₃ ⁺ [Bi₃I₁₂]^3?·2Me₂C=O (VI), [Ph₃BuP] ₂ ⁺ [Bi₂I₈·₂Me₂C=O]^2? (VII), and [Ph₃BuP] ₂ ⁺ [Bi₂I₈·2Me₂S=O]^2? (VIII) were obtained by reactions of bismuth iodide with ammonium and phosphonium iodides in acetone, pyridine, or dimethyl sulfoxide.     

Crystal structure of (C2H7N4O)2[UO2(C2O4)2(H2O)]

The single crystals of (C₂H₇N₄O)₂[UO₂(C₂O₄)₂(H₂O)] were studied by X-ray diffraction. The crystals are monoclinic, space group Pn, Z = 2, unit cell parameters: a = 9.4123(2) Å, b = 8.4591(2) Å, c = 11.8740(3) Å, β = 105.500(10)°, V = 911.02(4) ų. The main structural units of the crystals of I are islet complex groups [UO₂(C₂O₄)₂(H₂O)]^2? corresponding to the crystal chemical group AB ₂ ⁰¹ M¹ (A = UO UO ₂ ²⁺ , B⁰¹ = C₂O ₄ ^2? , M = H₂O) of uranyl complexes. Uranium-containing mononuclear complexes are connected into a three-dimensional framework through the electrostatic interactions and hydrogen bonding system involving carbamyolguanidinium ions.     

Solubility characteristics of poly(ethylene oxide): Effect of molecular weight,end groups and temperature

The general solvation equation $${\text{Log }}L = c + r \cdot R_2 + s \cdot \pi _2^{\text{H}} + a \cdot \alpha _2^{\text{H}} + b \cdot \beta _2^{\text{H}} + l \cdot \log {\text{ }}L^{16} $$ has been used to evaluate the effect of molecular weight, hydroxyl end groups and temperature on the solubility characteristics of poly(ethylene oxide), PEO. In this equationL is the gas-liquid partition coefficient of a series of probes on PEO, and the explanatory variables are solute properties describing the excess molar refraction,R ₂, the probe dipolarity-polarisability, π ₂ ^H , and the probe hydrogen-bond acidity and basicity, α ₂ ^H and β ₂ ^H .L ¹⁶ is the gas-liquid partition coefficient of the probe onn hexadecane at 298 K. Ther·R ₂ andl·logL ¹⁶ terms increased with increase in molecular weight whereas thes·π ₂ ^H and a α ₂ ^H terms decreased; in all cases theb·α ₂ ^H term was not significant. Since thes-constant is a measure of polymer polarity-polarisability, and thea-constant a measure of polymer basicity, we deduce that these polymer properties decrease with increasing molecular weight. Chains with molecular weight below 3000 showed a more rapid decrease in basicity compared to the higher molecular weight species. Thes·π ₂ ^H ,a·α ₂ ^H andl·logL ¹⁶ terms all decreased with increase in temperature. Finally, the contribution of the terminal hydroxyl groups to the total polymer basicity was evaluated and discussed.     

Synthesis, crystal structure, and thermal analysis of hexahydrogen dodecavanadate of composition [NH3 · H2O]6 · H6[Ca4V12O40] · 6H2O

Dihydrogen dodecavanadate of composition [NH₃ · H₂O]₆ · H₆[Ca₄V₁₂O₄₀] · 6H₂O was synthe-sized and studied by X-ray crystallography and TGA analyses. The crystals are cubic, space group I $\bar 4$ 3m;; unit cell parameters: a = 13.518(2) ?, V = 2470.4(3) ?³, ??_calc = 2.2334 g/cm³, Z = 2.     

Synthesis and crystal structure of Cs2[(UO2)2(C2O4)3] and Cs2[UO2(C3H2O4)2] · H2O

Cs₂[(UO₂)₂(C₂O₄)₃] (I) and Cs₂[UO₂(C₃H₂O₄)₂] · H₂O (II) have been synthesized and studied by X-ray diffraction. The crystals of complexes I and II are monoclinic: a = 8.1453(2) Å, b = 8.9831(2) Å, c = 11.3897(4) Å, β = 104.0950(10)°, V = 808.29(4) ų, space group P2₁/n, Z = 2, and R ₁ = 0.0255 for I and a = 9.6998(2) Å, b = 17.8686(3) Å, c = 8.2074(2) Å, β = 97.5780(10)°, V = 1410.10(5) ų, space group P2₁/c, Z = 4, and R ₁ = 0.0287 for II. The uranium-containing structural units of complexes I and II are [(UO₂)₂(C₂O₄)₃]^2? chains and [UO₂(C₃H₂O₄)₂] ₂ ^4? dimers, which belong to the AK _0.5 ⁰² T¹¹ and AT¹¹B⁰¹ crystallochemical groups (A = UO ₂ ²⁺ , K⁰² and T¹¹ = C₂O ₄ ^2? , T¹¹ and B⁰¹ = C₃H₂O ₄ ^2? ) of uranyl complexes.     

Crystal structure of enrofloxacinium tetrabromidodichloridostannate(IV) monohydrate

A new compound EnrH₃[SnBr_3.46Cl_2.54]·H₂O, where EnrH ₃ ²⁺ is the enrofloxacinium cation (C₁₉H₂₄FN₃O ₃ ²⁺ ), is synthesized and its crystal and molecular structure is determined. Crystallographic data for enrofloxacinium tetrabromidodichloridostannate(IV) monohydrate are as follows: a = 17.1262(19) Å, b = 10.3435(11) Å, c = 17.2582(19) Å, β = 119.203(1)°, V = 2640.5(4) ų, space group P2₁/c, Z = 4. Hydrogen bonds form a branched three-dimensional network linking EnrH ₃ ²⁺ , [SnBr_3.46Cl_2.54]^2?, and water molecules. The structure is also stabilized by the π-π interaction of EnrH ₃ ²⁺ aromatic rings.     

The role of the heteroatom (X?=?SiIV, PV, and SVI) on the reactivity of {��-[(H2O)RuIII(��-OH)2RuIII(H2O)][X n+W10O36]}(8?n)? with the O2 molecule

The mechanism of reaction of the di-Ru-substituted polyoxometalate, {??-[(H₂O)Ru^III(??-OH)₂Ru^III(H₂O)][X ⁿ⁺W₁₀O₃₆]}^(8?n)?, I_X, with O₂, i.e. I_X?+?O₂????{??-[(^·O)Ru^IV(??-OH)₂Ru^IV(O^·)][X ⁿ⁺W₁₀O₃₆]}^(8?n)??+?2H₂O, (1), was studied at the B3LYP density functional and self-consistent reaction field IEF-PCM (in aqueous solution) levels of theory. The effect of the nature of heteroatom X (where X?=?Si, P and, S) on the calculated energies and mechanism of the reaction (1) was elucidated. It was shown that the nature of X only slightly affects the reactivity of I_X with O₂, which is a 4-electron oxidation process. The overall reaction (1): (a) proceeds with moderate energy barriers for all studied X??s [the calculated rate-determining barriers are X?=?Si (18.7?kcal/mol)?<?S (20.6?kcal/mol)?<?P (27.2?kcal/mol) in water, and X?=?S (18.7?kcal/mol)?<?P (21.4?kcal/mol)?<?Si (23.1?kcal/mol) in the gas phase] and (b) is exothermic [by X?=?Si [28.7 (22.1) kcal/mol]?>?P [21.4 (9.8) kcal/mol]?>?S [12.3 (5.0) kcal/mol]. The resulting $ \left\{ {\gamma - \left[ {\left( {^{ \cdot } {\text{O}}} \right) {\text{Ru}}^{\text{IV}} \left( {\mu - {\text{OH}}} \right)_{2} {\text{Ru}}^{\text{IV}} \left( {{\text{O}}^{ \cdot } } \right)} \right]\left[ {{\text{X}}^{{{\text{n}} + }} {\text{W}}_{10} {\text{O}}_{36} } \right]} \right\}^{{\left( {8 - {\text{n}}} \right) - }} $ , VI_X, complex was found to have two Ru^IV?=?O^· units, rather than Ru^V?=?O units. The ??reverse?? reaction, i.e., water oxidation by VI_X is an endothermic process and unlikely to occur for X?=?Si and P, while it could occur for X?=?S under specific conditions. The lack of reactivity of VI_X biradical toward the water molecule leads to the formation of the stable [{Ru ₄ ^IV O₄(OH)₂(H₂O)₄}[(??-XW₁₀O₃₆]₂}^m? dimer. This conclusion is consistent with our experimental findings; previously we prepared the $ \left[ {\left\{ {{\text{Ru}}_{4}^{\text{IV}} {\text{O}}_{4} ({\text{OH}})_{2} \left( {{\text{H}}_{ 2} {\text{O}}} \right)_{4} } \right\}} \right[\left( {\gamma - {\text{XW}}_{10} {\text{O}}_{36} } \right]_{2} \}^{{{\text{m}} - }} $ dimers for X?=?Si (m?=?10) [Geletii et al. in Angew Chem Int Ed 47:3896?C3899, 2008 and J Am Chem Soc 131:17360?C17370, 2009] and P (m?=?8) [Besson et al. in Chem Comm 46:2784?C2786, 2010] and showed them to be very stable and efficient catalysts for the oxidation of water to O₂.     

Synthesis and X-ray diffraction study of K4[(UO2)2(C2O4)3(NCS)2] · 4H2O

Single crystals of K₄[(UO₂)₂(C₂O₄)₃(NCS)₂] · 4H₂O(I) have been synthesized and studied by X-ray diffraction. The crystals are monoclinic with the unit cell parameters a = 8.0226(7) Å, b = 14.9493(11) Å, c = 11.1670(9) Å, β = 98.299(3)°, space group P2₁/n, Z = 2, V = 1325.26(19) ų, R = 0.0186. The main structural units of the crystals of structure I are discrete binuclear groups [(UO₂)₂(C₂O₄)₃(NCS)₂]^4? belonging to the crystal-chemical group A₂K⁰²B ₂ ⁰¹ M ₂ ¹ (A =UO ₂ ²⁺ , K⁰² =C₂O ₄ ^2? , B⁰¹ =C₂O ₄ ^2? , M¹ = NCS^?) of the uranyl complexes. The uranium-containing complexes are linked into a three-dimensional framework through the potassium ions and a system of hydrogen bonds involving the outer-sphere water molecules.