Synthesis, structure and magnetic properties of new phosphates K2Mn0.5Ti1.5(PO4)3 and K2Co0.5Ti1.5(PO4)3 with the langbeinite structure

New complex phosphates of the general formula K₂M_0.5Ti_1.5(PO₄)₃ (M=Mn, Co) have been obtained from the melting mixture of KPO₃, K₄P₂O₇, TiO₂ and CoCO₃·mCo(OH)₂ or Mn(H₂PO₄)₂ by means of a flux technique. The synthesized phosphates have been characterized by the single-crystal X-ray diffraction and the FTIR-spectroscopy. The compounds crystallize in the cubic system with the space group P2₁3 and cell parameters a=9.9030(14) Å for K₂Mn_0.5Ti_1.5(PO₄)₃ and a=9.8445(12) Å for K₂Co_0.5Ti_1.5(PO₄)₃. Both phosphates are isostructural with the langbeinite mineral and contain four formula unit K₂M_0.5Ti_1.5(PO₄)₃ per unit cell. The structure can be described using [M₂(PO₄)₃] framework composed of two [MO₆] octahedra interlinked via three [PO₄] tetrahedra. The Curie-Weiss-type behavior is observed in the magnetic susceptibility.     

Synthesis and characterization of phosphates in the pseudo‐ternary melted systems Cs2O‐P2O5‐MIIO (MII – alkaline earth)

The crystallization of alkali‐earth phosphates in the melts of Cs₂O‐P₂O₅‐M^IIO (M^II – Ca, Sr, Ba) pseudo‐ternary systems have been investigated at various Cs/P molar ratios and at fixed value of M^II/P equal to 0.15. Type of the phosphate which crystallizes in melts depends on the Cs/P initial ratio. Crystallization fields of CsM^IIP₃O₉, M^II₂P₂O₇ and Cs₂M^IIP₂O₇ were briefly investigated and characterized. The new diphosphate Cs₂CaP₂O₇ has been obtained and investigated by the single crystal and powder X‐ray diffraction and FTIR‐ spectroscopy. It crystallizes in C 2/m space group, with the following parameters of the monoclinic cell: a = 10.261(2), b = 5.9316(12), c = 7.2404(14) Å, β = 118.54(3)°. The architecture of [CaP₂O₇]^2‐ anionic sublattice, which is built up from [CaO₆] octahedra and [P₂O₇] bitetrahedra, interlinked via the common oxygen vertices, gives rise to formation of hexagonal tunnels along crystallographic direction b, where caesium atoms are located. One of the most remarkable features of the structure is specific positional disorder of the diphosphate group, which is connected with the existence of two equiprobable half‐occupied sites of the bridging oxygen. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Complexation of Cyanine Dyes of the Tetrazolo[5,1-a]isoindole Series with Potassium Hexacyanoferrate(III) and Tetracyanonickelate(II)

The interaction of K₃[Fe(CN)₆] and K₂[Ni(CN)₄] with cyanine dyes of the tetrazoloisoindole series in nonaqueous media was established. This process involved both ion-exchange reactions and several other interactions. Four compounds were isolated and studied by electronic absorption spectroscopy, IR spectro-scopy, and mass spectrometry.     

A disordered cerium(IV) phosphate with a tunnel structure,K4CeZr(PO4)4

Tetra­potassium cerium(IV) zirconium tetra­kis­(mono­phos­phate) crystallizes in the tetra­gonal system (space group I4₁/amd). A complex disorder in K₄CeZr(PO₄)₄ involves the mixing of Ce and Zr atoms on a single site with m2 symmetry and the splitting of P‐ and O‐atom positions, equivalent to a rotation of the phosphate groups, to yield eight‐ and sixfold coordination environments around Ce and Zr, respectively. The K atoms are located in tunnels running parallel to the a and b axes.     

Structure and polymorphism of complex phosphates prepared from fluxes of the Na2O-P2O5-Fe2O3-Nb2O5 system

The phase formation of complex phosphates in the Na₂O-P₂O₅-Fe₂O₃-Nb₂O₅ flux system was studied in the ranges of sodium-to-phosphorus ratios of 0.7–1.2 and iron-to-niobium ratios of 0.9–2.7. The crystallization region and crystallization conditions for the compounds of composition Na_3?2x Fe_2-x Nb_x(PO₄)₃ (0.8 ≤ x < 1.2) were found. These compounds can be prepared in two (hexagonal and monoclinic) polymorphs. Single-crystal X-ray diffraction experiments were carried out for hexagonal NaFeNb(PO₄)₃ (space group $R\bar 3$ c, a = 8.590 Å, c = 22.013 Å). The polymorphism in Na_3-2x Fe_2-x Nb_x(PO₄)₃ complex phosphates is considered as dependent on the preparation parameters.     

Long-time dynamics of Rouse-Zimm polymers in dilute solutions with hydrodynamic memory

The dynamics of flexible polymers in dilute solutions is studied taking into account the hydrodynamic memory, as a consequence of fluid inertia. As distinct from the Rouse-Zimm (RZ) theory, the Boussinesq friction force acts on the monomers (beads) instead of the Stokes force, and the motion of the solvent is governed by the nonstationary Navier-Stokes equations. The obtained generalized RZ equation is solved approximately using the preaveraging of the Oseen tensor. It is shown that the time correlation functions describing the polymer motion essentially differ from those in the RZ model. The mean-square displacement (MSD) of the polymer coil is at short times approximately t(2) (instead of approximately t). At long times the MSD contains additional (to the Einstein term) contributions, the leading of which is approximately t. The relaxation of the internal normal modes of the polymer differs from the traditional exponential decay. It is displayed in the long-time tails of their correlation functions, the longest lived being approximately t(-3/2) in the Rouse limit and t(-5/2) in the Zimm case, when the hydrodynamic interaction is strong. It is discussed that the found peculiarities, in particular, an effectively slower diffusion of the polymer coil, should be observable in dynamic scattering experiments.     

On the vibration spectra of vesicle-like droplets: The effects of membrane density fluctuations

The dynamics of vesicle-like droplets is studied within the Helfrich’s concept of interfacial elasticity. The droplet shape fluctuations are accompanied with the membrane density changes. As distinct from the previous theories, the (linearized) hydrodynamic and boundary equations contain inertial terms and are solved exactly. Using the continuity equation for the interface, the secular equation for the vibration frequencies is obtained. Its analysis results in the prediction of a couple of relaxation modes that exist for any finite compressibility of the membrane, and a higher frequency mode determined mainly by the membrane density and compressibility. This work was supported by the grant 1/4387/97 (VEGA, Slovak Republic).     

Phase formation in molten system (Na/K)2O‐TiO2‐P2O5. Crystal structures of NASICON and langbeinite‐related phosphates (K/Na)1+xTi2(PO4)3 (x = 0 and 0.357)

Crystallization of high temperature self‐flux of system Na₂O‐K₂O‐TiO₂‐P₂O₅ was investigated at different molar ratios (Na+K)/P = 0.9; 1.0 or 1.2 and Na/K = 1.0 or 2.0 over the temperature range 1000–650°C. The conditions of formation of complex phosphates K_0.10Na_0.90Ti₂(PO₄)₃ (NASICON‐related) and K_0.877Na_0.48Ti^ІІІ_0.357Ti^ІV_1.643(PO₄)₃ (langbeinite‐related) have been established. The new obtained compounds were investigated using FTIR‐spectroscopy, powder and single crystal X‐ray diffraction and optical microscopy methods. The influence of alkaline metal nature on the structure formation of complex phosphates in the high temperature self‐fluxes is discussed.     

K2M(III)2(M(VI)O4)(PO4)2 (M(III) = Fe, Sc; M(VI) = Mo, W), novel members of the lagbeinite-related family: synthesis, structure, and magnetic properties

The possibility of PO(4)(3-) for MoO(4)(2-) partial substitution in the langbeinite framework has been studied by exploration of the K-Fe(Sc)-Mo(W)-P-O systems using the high-temperature solution method. It was shown that 1/3PO(4)(3-) for MoO(4)(2-) substitution leads to formation of three novel compounds K(2)Fe(MoO(4))(PO(4))(2), K(2)Sc(MoO(4))(PO(4))(2), and K(2)Sc(WO(4))(PO(4))(2) with slightly increased lattice parameters and significant distortion of the anion tetrahedra without structure changes. In contrast, the antiferromagnetic structure is modified by substitution in the low-temperature region. The structural peculiarities are discussed in light of bond-valence sums calculations.