Analysis of phase transition pathways in X3H(SO4)2 (X=Rb, NH4, K, Na): variable temperature single-crystal X-ray diffraction studies

Evaluation of phase transitions in a series of hydrogen sulfates (Rb3H(SO4)2, (NH4)3H(SO4)2, K3 H(SO4)2, and Na3H(SO4)2) based on the single-crystal structure analysis has revealed the exact nature of such transitions and has sorted out the various ambiguities involved in earlier literature. Rb3H(SO4)2 at 293 K is C2/c. It is isostructural to its ammonium analogue, (NH4)3H(SO4)2, at room temperature. However, the variable temperature single-crystal diffraction studies indicate that the phase transition mechanism is different. When cooled to 100 K, the structure of Rb3H(SO4)2 remains C2/c. When heated to 350 K, it transforms to C2/m (with double the volume at room temperature), which changes to C2/c (with 4 times the volume at room temperature) at 425 K. The high-temperature (420 K) structural phase transition in (NH4)3H(SO4)2 is shown to be Rm. The structure of Na3H(SO4)2 remains invariant (P21/c) throughout the range of 100-500 K except for the usual contraction of the unit cell at 100 K and expansion at 500 K. The structural phase transitions with temperature for the compound K3H(SO4)2 are very different from those claimed in earlier literature. The hydrogen atom participating in the crucial hydrogen bond joining the two sulfate tetrahedra controls the structural phase transitions at low temperatures in all four compounds. The distortion of the SO4 tetrahedra and the coordination around the metal atom sites control the phase evolution in the Rb compound, while the Na and K analogues show no phase transitions at high temperature, and the NH4 system transforms to a higher symmetry space group resulting in a disorder of the sulfate moiety.     

Thermodynamic studies on the ferroelectric phase transition in neutron irradiated (LixK1−x)2SO4 crystals at high temperature

Thermodynamic studies of (Li_xK_1?x)₂SO₄, LKS, mixed crystals have been made in the concentration range (x=0.1, 0.2, ...,x=0.5). The thermal behaviour has been investigated by differential thermal analysis, DTA, and differential scanning calorimeter, DSC, in the vicinity of high temperature phases. Also, the effect of the thermal neutron irradiations on the thermal properties of mixed crystals was studied. The results showed a change in the transition temperatureT _c, as well as the value of specific heatC _p at transition temperature, due to the change of stoichiometric ratio and radiation doses. The change of enthalpy and entropy of mixed crystals have been estimated numerically.     

Neutron scattering studies of K(3)H(SO(4))(2) and K(3)D(SO(4))(2): The particle-in-a-box model for the quantum phase transition

In the crystal of K(3)H(SO(4))(2) or K(3)D(SO(4))(2), dimers SO(4)???H???SO(4) or SO(4)???D???SO(4) are linked by strong centrosymmetric hydrogen or deuterium bonds whose O???O length is ≈2.50 A?. We address two open questions. (i) Are H or D sites split or not? (ii) Is there any structural counterpart to the phase transition observed for K(3)D(SO(4))(2) at T(c) ≈ 85.5 K, which does not exist for K(3)H(SO(4))(2)? Neutron diffraction by single-crystals at cryogenic or room temperature reveals no structural transition and no resolvable splitting of H or D sites. However, the width of the probability densities suggest unresolved splitting of the wavefunctions suggesting rigid entities H(L1∕2) -H(R1∕2) or D(L1∕2) -D(R1∕2) whose separation lengths are l(H) ≈ 0.16 A? or l(D) ≈ 0.25 A?. The vibrational eigenstates for the center of mass of H(L1∕2) -H(R1∕2) revealed by inelastic neutron scattering are amenable to a square-well and we suppose the same potential holds for D(L1∕2) -D(R1∕2). In order to explain dielectric and calorimetric measurements of mixed crystals K(3)D((1 - ρ))H(ρ)(SO(4))(2) (0 ≤ ρ ≤ 1), we replace the classical notion of order-disorder by the quantum notion of discernible (e.g., D(L1∕2) -D(R1∕2)) or indiscernible (e.g., H(L1∕2) -H(R1∕2)) components depending on the separation length of the split wavefunction. The discernible-indiscernible isostructural transition at finite temperatures is induced by a thermal pure quantum state or at 0 K by ρ.     

Computer-assisted structure simulation, synthesis, and phase formation of molybdophosphates A1−x Zr2(PO4 3−x (MoO4)x (A is an alkali metal)

Structure simulation is performed for molybdophates of variable composition A_1?x Zr₂(PO₄)_3?x (MoO₄)_x, where A is Na (0≤x≤0.6), K (0≤x≤0.6), K (0≤x≤0.3), Rb (0≤x≤0.2), or Cs (0≤x≤0.1), using the minimization of the interatomic interaction energy; these molybdophosphates crystallize in the NaZr₂(PO₄)₃ (NZP) structure type. The results of the computer-assisted structure simulation are verified by the synthesis of the molybdophosphates and their characterization by X-ray powder diffraction and IR spectroscopy. The crystallization field of the NZP molybdophosphate shrinks as the alkali cation size increases. The key factors that govern the stability of the NZP structure in alkali zirconium molybdophosphates are determined.     

Electronic structure and normal vibrations of CH3(OCH2CH2)nOCH3-M+-CF3SO3- (n = 2-4, M = Li, Na, and K)

Electronic structure and the vibrational frequencies of CH(3)(OCH(2)CH(2))(n)OCH(3)-M(+)-CF(3)SO(3)(-) (n = 2-4, M = Li, Na, and K) complexes have been derived from ab initio Hartree-Fock calculations. The metal ion shows varying coordination from 5 to 7 in these complexes. In tetraglyme-lithium triflate, Li(+) binds to one of the oxygens of CF(3)SO(3)(-) (triflate or Tf(-)) unlike for potassium or sodium ions, which possess bidentate coordination. Structures of glyme-MTf complexes thus derived agree well with those determined from X-ray diffraction experiments. The metal ion binds more strongly to ether oxygens of tetraglyme than its di- or triglyme analogues and engenders contraction of SO (for oxygens binding to metal ion) bonds with consequent frequency upshift for the corresponding vibration in the complex relative to those in the free MTf ion pairs. Complexation of the diglyme with LiTf engenders the largest downshift (91 cm(-1)) for the SO(2) stretching vibration of the free anion, which suggests stronger binding of lithium to the diglyme than the tri- (79 cm(-1)) or tetraglyme (70 cm(-1)). A frequency shift in the opposite direction for the SO (where oxygens do not coordinate to the metal) and CF(3) stretchings, which stems from the ion-polymer and anion-ion interactions, has been noticed. These frequency shifts have been analyzed using natural bond orbital analysis and difference electron density maps coupled with molecular electron density topography.     

Cs2.91Na1.34Fe3+0.25[Fe3O(SO4)6(H2O)3]·5H2O,a member of the Maus's salt family

The title compound, tricaesium sodium iron(III) μ₃‐oxido‐hexa‐μ₂‐sulfato‐tris[aquairon(III)] pentahydrate, Cs_2.91Na_1.34Fe³⁺_0.25[Fe₃O(SO₄)₆(H₂O)₃]·5H₂O, belongs to the family of Maus's salts, K₅[Fe₃O(SO₄)₆(H₂O)₃]·6H₂O, which is based on the triaqua‐μ₃‐oxido‐hexa‐μ‐sulfato‐triferrate(III) anion, [Fe₃O(SO₄)₆(H₂O)₃]⁵⁻, with Fe in a characteristically distorted octahedral coordination environment, sharing a common corner via an oxide O atom. Cs in four different cation sites, Na in three different cation sites and five water molecules link the anions in three dimensions and set up a crystal structure in which those parts parallel to (001) and within 0.05 < z < 0.95 have a distinct trigonal pseudosymmetry, whereas the cation arrangement and bonding near z∼ 0 generate a clear‐cut noncentrosymmetric polar edifice with the monoclinic space group C2. The structure shows some cation disorder in the region near z ∼ , where one Na atom in octahedral coordination is partly substituted by Fe³⁺, and a Cs atom is substituted by small amounts of Na on a separate nearby site. One Na atom, located on a twofold axis at z = 0 and tetrahedrally coordinated by four sulfate O atoms of two [Fe₃O(SO₄)₆(H₂O)₃]⁵⁻ units, plays a key role in generating the noncentrosymmetric structure. Three of the seven different cation sites are on twofold axes (one Na⁺ site and two Cs⁺ sites), and all other atoms of the structure are in general positions.     

Novel tantalum phosphate Na13Sr2Ta2(PO4)9: synthesis,crystal structure,DFT calculations and Dy3+‐activated fluorescence performance

A new tantalum phosphate, tridecasodium distrontium ditantalum nonaphosphate, Na₁₃Sr₂Ta₂(PO₄)₉, was prepared using the high‐temperature flux method. The structure can be described as a three‐dimensional open framework containing isolated [Ta^V₂(PO₄)₉]¹⁷⁻ units that are interlocked by Na and Sr ions. Band structure studies by the first‐principles method revealed that Na₁₃Sr₂Ta₂(PO₄)₉ is an insulator with an indirect band gap of 4.78 eV, which makes it suitable as a luminescent host matrix. A series of solid solutions, i.e. Na₁₃Sr_2–xTa₂(PO₄)₉:xDy³⁺ (x = 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12 and 0.14), were prepared and their photoluminescence properties studied. Under 350 nm light excitation, these emit two typical emissions of the Dy³⁺ ion, i.e. the ⁴F_9/2→⁶H_15/2 transition centred at 476 nm and the ⁴F_9/2→⁶H_13/2 transition centred at 570 nm.     

Facile synthesis of Fe3O4/MoS2 nanohybrid for solid phase extraction of Ag(I) and Pb(II): kinetic,isotherm and thermodynamic studies

Recently, MoS₂ with abundant electron density in its structure attracted more attention as an adsorbent for environmental remediation. However, hard manipulation of target solution owing to high dispersibility in aqueous media restricts its application as adsorbent. Preparation of Fe₃O₄/MoS₂ nanohybrid can solve this problem. Also, this nanohybrid improves adsorption capacities of target ions. In this work, Fe₃O₄ nanoparticles, MoS₂ nanosheets and hybrid of these two were synthesised and then characterised by X-ray diffraction, energy-dispersive X-ray spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, Fourier transforms infrared spectra, Brunauer–Emmett–Teller surface area and vibrating sample magnetometer. Subsequently, adsorption of Ag(I) and Pb(II) ions from aqueous solution by these three adsorbents was examined in detail and compared with each other while the adsorption conditions including the pH value, contact time, dosage of sorbent, elution conditions and interfering ions have been optimised. According to obtained results, prepared nanohybrid showed enhanced adsorption capacities for both ions relative to naked Fe₃O₄ and MoS₂. The limits of detection for Ag(I) and Pb(II) were calculated as 0.49 µg L^?1 and 2.7 µg L^?1, respectively, and the relative standard deviation percentages (n = 5) for Ag(I) and Pb(II) were 2.8%, and 3.0%, respectively. Furthermore, the preconcentration factors were 300 and 75 for Ag(I) and Pb(II) ions, respectively. Moreover, kinetic studies showed that pseudo-second-order model can better describe target analytes adsorption properties by every three adsorbents. Regeneration of the adsorbents was performed with HCl/thiourea mixture.     

Polyoxometalates with internal cavities: redox activity, basicity, and cation encapsulation in [Xn+P5W30O110](15-n)- Preyssler complexes, with X = Na+, Ca2+, Y3+, La3+, Ce3+, and Th4+

The Preyssler anion, of general formula [Xn+P5W30O110](15-n)-, is the smallest polyoxometalate (POM) with an internal cavity allowing cation exchange with the solution. The Preyssler anion features a rich chemistry evidenced by its ability to accept electrons at low potentials, to selectively capture various metal cations, and to undergo acid-base reactions. A deep understanding of these topics is herein provided by means of DFT calculations on the title series of compounds. We evaluate the energetics of the release/encapsulation process for several Xn+ cations and identify the effect of the encapsulated ion on the properties of the Preyssler anion. We revisit the relationship between the internal cation charge and the electrochemical behavior of the POM. A linear dependence between the first one-electron reduction energies and the encapsulated Xn+ charge is found, with a slope of 48 mV per unit charge. The protonation also shifts the reduction potential to more positive values, but the effect is much larger. In connection to this, the last proton's pKa = 2 for the Na+ derivative was estimated to be in reasonable agreement with experiment. The electronic structure of lanthanide derivatives is more complex than conventional POM structures. The reduction energy for the CeIV-Preyssler + 1e- --> CeIII-Preyssler process was computed to be more exothermic than that of very oxidant species such as S2Mo18O624-.     

A new class of functionalized polyoxometalates: synthesis, structure and preliminary antitumor activity studies of three arylimido substituted hexamolybdates bearing a strong electron-withdrawing nitro group, (Bu4N)2[Mo6O18([triple bond]NAr)] (Ar = 3-NO2-C6H4, 2-CH3-4-NO2-C6H3, 2-CH3-5-NO2-C6H3)

Three novel mono-functionalized arylimido derivatives of hexamolybdate bearing the strongest electron-withdrawing nitro group, (Bu(4)N)(2)[Mo(6)O(18)([triple bond, length as m-dash]NAr)] (, and ), have been synthesized for the first time by an improved reaction of octamolybdate ion and 3-nitroaniline hydrochloride, 2-methyl-4-nitroaniline hydrochloride and 2-methyl-5-nitroaniline hydrochloride respectively with DCC (N,N'-dicyclohexylcarbodiimide) as a dehydrating agent. Complete assignments were achieved for the title compounds by elemental analysis, IR, (1)H NMR, UV/visible and single-crystal X-ray diffraction analyses. The preliminary antitumor activity test indicated that the title compounds have some effects on the cellular growth inhibition of K562 cells.     

Dissolution thermochemistry of alkali metal dianion salts (M2X1, M = Li+, Na+, and K+ with X = CO3(2-), SO4(2-), C8H8(2-), and B12H12(2-))

The dissolution Gibbs free energies (ΔG°(diss)) of salts (M(2)X(1)) have been calculated by density functional theory (DFT) with Conductor-like Polarizable Continuum Model (CPCM) solvation modeling. The absolute solvation free energies of the alkali metal cations (ΔG(solv)(M(+))) come from the literature, which coincide well with half reduction potential versus SHE data. For solvation free energies of dianions (ΔG(solv)(X(2-))), four different DFT functionals (B3LYP, PBE, BVP86, and M05-2X) were applied with three different sets of atomic radii (UFF, UAKS, and Pauling). Lattice free energies (ΔG(latt)) of salts were determined by three different approaches: (1) volumetric, (2) a cohesive Gibbs free energy (ΔG(coh)) plus gaseous dissociation free energy (ΔG(gas)), and (3) the Born-Haber cycle. The G4 level of theory, electron propagator theory, and stabilization by dielectric medium were used to calculate the second electron affinity to form the dianions CO(3)(2-) and SO(4)(2-). Only the M05-2X/Pauling combination with the three different methods for estimating ΔG(latt) yields the expected negative dissolution free energies (ΔG°(diss)) of M(2)SO(4). Salts with large dianions like M(2)C(8)H(8) and M(2)B(12)H(12) reveal the limitation of using static radii in the volumetric estimation of lattice energies. The value of ΔE(coh) was very dependent on the DFT functional used.     

Measurements of (p,,T,x) for {x CS2 + (1-x) Si(CH3)4}(1) from 198 to 298 K and pressures up to 104 MPa. Experimental results and derived thermodynamic properties

Molar densities have been measured by using an expansion technique at pressures up to 104 MPa and temperatures from 198 to 298 K for the mixture {x CS₂ + (1-x) Si(CH₃)₄}(1) over the whole composition range. Several thennodynamic properties (isothermal compressibility, thermal expansivity, and molar internal energy, enthalpy and entropy increments relative to liquid at saturation) have been directly obtained from the experimental densities. The isothermal compressibility and the thermal expansivity are both smooth functions of pressure, temperature and composition, although the isotherms of the thermal expansivity exhibit a characteristic crossover at high pressures. The intersection of isotherms of thermal expansivity seems to occur at a single point of the (p,α_p) diagram, showing a nearly linear dependence with the composition.     

Evidence for the first oxidative insertion of a transition metal into a digallane(4): synthesis, structural characterisation and EPR studies of [Cp2Zr(III){Ga[N(Ar)C(H)]2}2][Li(THF)4], Ar = C6H3Pr(i)2-2,6

Treatment of "ZrCp2" with the digallane(4), [{Ga[N(Ar)C(H)]2}2], Ar = C6H3Pri2-2,6, in the presence of excess Bu(n)Li leads to the first example of a gallyl-Group 4 complex, [Cp2Zr{Ga[N(Ar)C(H)]2}2][Li(THF)4], via an unprecedented oxidative insertion reaction; the paramagnetic complex has been characterised by X-ray crystallography and EPR spectroscopy.