New fluorinated polymers bearing pendant phosphonic groups for fuel cell membranes: Part 1 synthesis and characterizations of the fluorinated polymeric backbone

Radical copolymerizations of chlorotrifluoroethylene (CTFE) with vinyl ethers such as 2-chloroethyl vinyl ether (CEVE) and ethyl vinyl ether (EVE) were performed at 75 °C in the presence of peroxide initiator. Three copolymers were obtained and characterized by means of both NMR and elemental analysis. Then, the chlorine atoms in the side chains were converted into iodine atoms by nucleophilic substitution, which was monitored by ¹H NMR spectroscopy. A series of five copolymers with different amounts of iodine atoms in the side chains were thus obtained. These copolymers exhibited molecular weight values of about 25,000 g mol⁻¹, and the thermal analysis of the copolymers showed a starting degradation from about 220 °C. The T_g values were in the range of 34-41 °C and showed a linear dependence versus the content of iodine atoms.     

Trapping phosphate anions inside the [Ag4I] framework: Structure, bonding, and properties of Ag4I(PO4)

Orange-red Ag₄I(PO₄) crystallizes in the monoclinic system, space group P2₁/m (No. 11), with the unit cell dimensions a=9.0874(6) Å, b=6.8809(5) Å, c=11.1260(7) Å, β=109.450(1)°, and Z=4. The crystal structure is fully ordered; it comprises the silver-iodine three-dimensional positively charged framework hosting the tetrahedral PO₄³⁻ guest anions. The framework features high coordination numbers for iodine and manifold Ag-Ag bonds ranging from 3.01 to 3.46 Å. The Ag-Ag interaction is bonding, it involves silver 4d and 5s orbitals lying, together with the orbitals of iodine, just below the Fermi level. Though the orbitals of silver and iodine define the conducting properties of the title compound, the interaction between the framework and the guest anions is also important and is responsive to the number of the silver atoms surrounding the PO₄³⁻ tetrahedra. Ag₄I(PO₄) melts incongruently at 591 K and produces a mixture of the silver phosphate and an amorphous phase upon cooling. Pure Ag₄I(PO₄) is a poor conductor with a room temperature conductivity of 3×10⁻⁶ S m⁻¹. The discrepancies between the properties observed here and those reported previously in the literature are discussed.     

Interplay of Charge Transfer, Dimensionality, and Amide Hydrogen Bond Network Adaptability in TCNQF4 Complexes of EDO-TTF-CONH2 and EDT-TTF-CONH2

[EDO-TTF-CONH₂][TCNQF₄], triclinic system, space group P-1, a=8.2479(12) Å, b=12.282(2) Å, c=12.6842(18) Å, α=113.850(17)°, β=106.420(17)°, γ=90.284(19)°, V=1116.8(4) ų; and [EDT-TTF-CONH₂]₂[TCNQF₄], triclinic system, space group P-1, a=6.5858(9) Å, b=11.699(2) Å, c=12.2281(18) Å, α=104.000(19)°, β=93.611(17)°, γ=98.279(19)°, V=899.9(3) ų, whose π-donor molecules, (ethylenedioxo)-carbamoyltetrathiafulvalene and (ethylenedithio)-carbamoyltetrathiafulvalene, respectively, differ solely by the nature of the chalcogen atoms in their outer ethylene dichalcogeno bridge, yet form very different charge-transfer complexes with the same π-acceptor. [EDO-TTF-CONH₂^•+]₂ [TCNQF₄^•−]₂ is a diamagnetic insulating ionic salt with a three-dimensional rock-salt-type structure based on discrete dimers while in the semi-conducting mixed-valence complex, [EDT-TTF-CONH₂]₂^•+[TCNQF₄^•−], the mixed-valence dimers aggregate into infinite chains interspersed within parallel rows of non-interacting radical anions. It is shown how the robust and adaptable supramolecular amide hydrogen bond tweezers-like motifs common to the two solids simply comply to the 3-to-1 dimensionality reduction upon substitution of O for S.     

Crystal structures and photocatalysis of the triclinic polymorphs of BiNbO4 and BiTaO4

The high-temperature polymorphs of two photocatalytic materials, BiNbO₄ and BiTaO₄ were synthesized by the ceramic method. The crystal structures of these materials were determined by single-crystal X-ray diffraction. BiNbO₄ and BiTaO₄ crystallize into the triclinic system P1¯ (No. 2), with a=5.5376(4) Å, b=7.6184(3) Å, c=7.9324(36) Å, α=102.565(3)°, β=90.143(2)°, γ=92.788 (4)°, V=326.21 (5) Å³, Z=4 and a=5.931 (1) Å, b=7.672 (2) Å, c=7.786 (2) Å, α=102.94 (3)°, β=90.04 (3)° γ=93.53 (3)°, V=344.59 (1) Å³ and Z=4, respectively. The structures along the c-axis, consist of layers of [Bi₂O₂] units separated by puckered sheets of (Nb/Ta)O₆ octahedra. Photocatalytic studies on the degradation of dyes indicate selectivity of BiNbO₄ towards aromatics containing quinonic and azo functional groups.     

Synthesis crystal structure and ionic conductivity of Ca0.5Bi3V2O10 and Sr0.5Bi3V2O10

Two new compounds Ca_0.5Bi₃V₂O₁₀ and Sr_0.5Bi₃V₂O₁₀ have been synthesized in the ternary system: MO-Bi₂O₃-V₂O₅ system (M=M²⁺). The crystal structure of Sr_0.5Bi₃V₂O₁₀ has been determined from single crystal X-ray diffraction data, space group and Z=2, with cell parameters a=7.1453(3) Å, b=7.8921(3) Å, c=9.3297(3) Å, α=106.444(2)°, β=94.088(2)°, γ=112.445(2)°, V=456.72(4) Å³. Ca_0.5Bi₃V₂O₁₀ is isostructural with Sr_0.5Bi₃V₂O₁₀, with, a=7.0810(2) Å, b=7.8447(2) Å, c=9.3607(2) Å, α=106.202(1)°, β=94.572(1)°, γ=112.659(1)°, V=450.38(2) Å³ and its structure has been refined by Rietveld method using powder X-ray data. The crystal structure consists of infinite chains of (Bi₂O₂) along c-axis formed by linkage of BiO₈ and BiO₆ polyhedra interconnected by MO₈ polyhedra forming 2D layers in ac plane. The vanadate tetrahedra are sandwiched between these layers. Conductivity measurements give a maximum conductivity value of 4.54×10⁻⁵ and 3.63×10⁻⁵ S cm⁻¹ for Ca_0.5Bi₃V₂O₁₀ and Sr_0.5Bi₃V₂O₁₀, respectively at 725 °C.     

Polyoxometalate-based eight-connected self-catenated network and fivefold interpenetrating framework

Two entangled compounds [(bpy)₆Cu^I₆Cl₃(Mo^VW₅O₁₉)] (1) and [(bpy)₇Cu^I₇Cl₂(BW₁₂O₄₀)]·H₂O (2) (bpy=4,4′-bipyridine), have been successfully synthesized under hydrothermal conditions and characterized by element analysis, IR spectroscopy, thermal gravimetric analysis, X-ray photoelectron spectroscopy, and single crystal X-ray diffraction analyses. Compound 1 represents the first eight-connected self-penetrating network constructed from cuprous chloride clusters [Cu₆Cl₃] and Lindquist-type polyoxoanions. Compound 2 exhibits an interesting fivefold interpenetrating network consisting of Keggin polyoxoanions and Cu⁺-metal-organic framework. Crystal data of the two compounds are following: 1, triclinic, , a=11.502(2) Å, b=13.069(3) Å, c=13.296(3) Å, α=90.55(3)°, β=113.74(3)°, γ=110.48(3)°, Z=1; 2, triclinic, , a=12.341(3) Å, b=13.119(3) Å, c=15.367(3) Å, α=99.12(3)°, β=90.53(3)°, γ=104.49(3)°, Z=1.     

Structural and vibrational characterization of [KrF][AuF6] and α-[O2][AuF6] using single crystal X-ray diffraction, Raman spectroscopy and electron structure calculations

The salt [KrF][AuF₆] has been prepared by the direct oxidation of gold powder in anhydrous HF at 20 °C using the potent oxidative fluorinating agent KrF₂. The KrF⁺ salt readily oxidizes molecular oxygen at ambient temperature to yield [O₂][AuF₆]. Variable temperature Raman spectroscopy has been used to identify a reversible phase transition in [O₂][AuF₆], which occurs between −114 and −118 °C. Single crystal X-ray diffraction has been used to characterize the low-temperature, α-phase of [O₂][AuF₆]. The phase transition is attributed to ordering of the O₂⁺ cation in the crystal lattice, which is accompanied by minor distortions of the AuF₆⁻ anion. The α-phase of [O₂][AuF₆] crystallizes in the triclinic space group , with a=4.935(6) Å, b=4.980(6) Å, c=5.013(6) Å, α=101.18(1)°, β=90.75(2)°, γ=101.98(2)°, V=342.97 Å³, Z=1, and R₁=0.0481 at −122 °C. The structure of the precursor, [KrF][AuF₆], has also been determined by single crystal X-ray diffraction and crystallizes in the monoclinic space group Cc with a=7.992(3) Å, b=7.084(3) Å, c=10.721(4) Å, β=105.58(1)°, V=584.8(4) Å³, Z=4 and R₁=0.0389 at −125 °C. The KrF⁺ and AuF₆⁻ ions interact by means of a FKr---FAu fluorine bridge that is bent by 125.3(7)° about the bridge fluorine. The KrF_t and Kr---F_b bond lengths in [KrF][AuF₆] were determined to be 1.76(1) and 2.15(1) Å, respectively. The energy minimized structures of the [KrF][AuF₆] ion-pair and the AuF₆⁻ anion have been determined at the Hartree-Fock (HF), MP2 and local density functional (LDF) levels of theory. These calculations have also been used to assign the vibrational spectrum of the [KrF][AuF₆] ion-pair in greater detail and to reassign the vibrational spectrum of the AuF₆⁻ anion.     

Atom transfer radical polymerization of 2-methoxy ethyl acrylate and its block copolymerization with acrylonitrile

2-Methoxy ethyl acrylate (MEA), a functional monomer was homopolymerized using atom transfer radical polymerization (ATRP) technique with methyl 2-bromopropionate (MBP) as initiator and CuBr/N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) as catalyst system; polymerization was conducted in bulk at 60 °C and livingness was established by chain extension reaction. The kinetics as well as molecular weight distribution data indicated towards the controlled nature of polymerization. The initiator efficiency and the effect of initiator concentration on the rate of polymerization were investigated. The polymerization remained well-controlled even at low catalyst concentration of 10% relative to initiator. The influence of different solvents, viz. ethylene carbonate and toluene on the polymerization was investigated. End-group analysis for the determination of high degree of functionality of PMEA was determined with the help of ¹³C{¹H} NMR spectra. Chain extension experiment was conducted with PMEA macroinitiator for ATRP of acrylonitrile (AN) in ethylene carbonate at 70 °C using CuCl/bpy as catalyst system. The composition of individual blocks in PMEA-b-PAN copolymers was determined using ¹H NMR spectra.     

Synthesis and characterization of two-dimensional fluorinated metal phosphates incorporating 2,2′-bipyridine ligands: M2F2(2,2′-bpy)(HPO4)2(H2O) (M=Fe, Ga)

Two fluorinated metal phosphates, M₂F₂(2,2′-bpy)(HPO₄)₂(H₂O) (M=Fe, Ga), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility. The two compounds are isostructural and crystallize in the triclinic space group , a=7.6595(8)Å, b=10.101(1)Å, c=11.260(1)Å, α=107.555(2)°, β=105.174(2)°, γ=98.975(2)°, V=775.1(2)ų and Z=2 for the Fe compound, and a=7.5816(6)Å, b=9.9943(7)Å, c=11.1742(8)Å, α=107.333(1)°, β=105.014(1)°, γ=99.261(1)° and V=754.2(2)ų for the Ga compound. They are the first fluorinated metal phosphates which incorporate 2,2′-bipyridine ligands. The structure consists of edge-sharing octahedral dimers with the composition Fe₂F₄(H₂O)₂O₄ and discrete FeN₂O₄ octahedra, which are linked into two-dimensional sheets through corner-sharing phosphate tetrahedra. The 2,2′-bpy ligands bind in a bidentate fashion to the metal atoms and project into interlamellar region. The layers are extended into a three-dimensional supramolecular array via π-π stacking interactions of the 2,2′-bpy ligands. Magnetic susceptibility of the iron compound confirms the presence of Fe^III.     

Potentiometric studies of the thermodynamics of iodine disproportionation from 4 to 209°C

The equilibrium constant for the disproportionation of iodine in aqueous solution was determined as a function of temperature from 3.8 to 209.0°C using emf measurements in low ionic strength media. The equilibrium constant and associated molal thermodynamic quantities at 25°C are: K₁=1.17±0.62×10^–47, H^o=273±3 kJ-mol^–1, S^o=16±9 J-K^–1-mol^–1, and C _p ^o =–1802±41 J-K^–1-mol^–1. Although the value of K₁ is in excellent agreement with a previous emf measurement at 25°C, these results conflict with the corresponding parameters obtained from the NBS tables. Moreover, at temperatures above ca. 100°C, our measured values for the equilibrium constant diverge strongly from all previous estimates and predictions.     

High-pressure synthesis and structural characterization of three new polyphosphides, α-SrP3, BaP8, and LaP5

Three novel metal polyphosphides, α-SrP₃, BaP₈, and LaP₅, were prepared in BN crucibles by the reaction of the respective stoichiometric mixtures under a high pressure of 3 GPa at 950-1000°C. Their crystal structures were determined from single-crystal X-ray data (α-SrP₃: space group C2/m, a=9.199(6) Å, b=7.288(3) Å, c=5.690(3) Å, β=113.45(4)°, Z=4, R₁/wR₂=0.0684/0.1180 for 471 observed reflections and 22 variables; BaP₈: space group P−1, a=6.762(2) Å, b=7.233(2) Å, c=8.567(2) Å, α=86.32(2)°, β=84.31(2)°, γ=70.40(2)°, Z=2, R₁/wR₂=0.0476/0.1255 for 2702 observed reflections and 82 variables; LaP₅: space group P2₁/m, a=4.885(1) Å, b=9.673(3) Å, c=5.577(2) Å, β=105.32(2)°, Z=2, R₁/wR₂=0.0391/0.1034 for 1272 observed reflections and 31 variables). α-SrP₃ is isostructural with SrAs₃ and the crystal structure consists of two-dimensional puckered polyanionic layers _∞²[P₃]²⁻ that stack along the c-axis yielding channels occupied by Sr²⁺ counterions. BaP₈ crystallizes in a new structure type which contains a three-dimensional infinite polyanionic framework _∞³[P₃]²⁻, with large channels hosting the barium cations. LaP₅ is a layered compound containing _∞²[P₅]³⁻ polyanionic layers separated by La³⁺ ions. All three compounds exhibit expected diamagnetic behaviors.     

Synthesis, structure and magnetic properties of the pillared perovskites La5Re3MO16(M=Mg, Fe, Co, Ni)

Four new compounds La₅Re₃MgO₁₆ La₅Re₃FeO₁₆ La₅Re₃CoO₁₆ La₅Re₃NiO₁₆ have been prepared by solid-state reaction and characterized by X-ray and neutron powder diffraction and SQUID magnetometry. Rietveld refinement revealed that the four compounds are isostructural with La₅Re₃MnO₁₆ and crystallize in space group with cell parameters a=7.9370(3), 7.9553(5), 7.9694(7), and 7.9383(4) Å; b=7.9998(3), 7.9960(6), 8.0071(8), and 7.9983(5) Å; c=10.1729(4), 10.1895(7), 10.182(1), and 10.1732(6) Å; α=90.190(3)°, 90.270(3)°, 90.248(4) °, 90.287(3)°; β=94.886(2)°, 95.082(3)°, 94.980(4)°, 94.864(3)°; γ=89.971(4)°, 90.001(5)°, 89.983(6)°, 89.968(4)° for Mg, Fe, Co, and Ni, respectively. The structures are related to a layered perovskite. The layers of corner-sharing octahedra Re⁵⁺M²⁺O₆ (M²⁺=Mg, Fe, Co, Ni) are pillared by diamagnetic edge-sharing octahedra dimers, Re₂O₁₀, involving a Re=Re double bond. Three crystallographically independent lanthanum atoms occupy the three-dimensional interstices. All compounds obey the Curie-Weiss law at sufficiently high temperatures with Curie constants or effective magnetic moments near the expected values for the combination of Re⁵⁺(S=1) and M²⁺(S=0, 2, 3/2, 1 for Mg, Fe, Co, and Ni, respectively). Weiss constants, θ_C, are negative (−575, −84, −71, and −217 K for Mg, Fe, Co, and Ni, respectively) indicating the predominance of antiferromagnetic exchange coupling. The phases for M=Fe, Co and Ni show long-range order at 155, 33, 36 and 14 K, respectively. Neutron diffraction discloses a magnetic structure for the Fe series member consisting of ferrimagnetic perovskite layers coupled antiparallel along the stacking c-axis, direction which is consistent with the magnetic structure found recently for La₅Re₃MnO₁₆.     

Synthesis and characterization of the mixed ligand coordination polymer CPO-5

The synthesis and crystal structures of a novel coordination polymer and its high-temperature variant are described. The as-synthesized material (CPO-5-as), of composition Zn(4,4′-bipyridine)(4,4′-biphenyldicarboxylate)·3H₂O, crystallizes in the triclinic space group P-1 (No. 2) with a=11.0197(2), b=14.2975(3), c=7.6586(1) Å, α=95.9760(9)°, β=108.026(1)°, γ=91.373(1)° and V=1139.16(4) Å³. CPO-5-as is composed of tetrahedral zinc centers that are connected by the organic linkers to give five independent, interpenetrating diamond networks. In the structure, there is additional space for channels that are filled with three water molecules. These water molecules can be removed, leading to an anhydrous variant at 130^oC. CPO-5-130, of composition Zn(4,4′-bipyridine)(4,4′-biphenyldicarboxylate), crystallizes in the triclinic space group P-1 (No. 2) with a=11.1844(6), b=14.0497(7), c=7.7198(3) Å, α=96.917(2)°, β=109.527(2)°, γ=89.115(3)° and V=1134.6(1) Å³. The structure of the five interpenetrating networks is virtually unchanged after the dehydration resulting in CPO-5-130 being a porous structure with an estimated free volume of 19.8%.     

A novel two-dimensional β-octamolybdate supported alkaline-earth metal complex: [Ba(DMF)2(H2O)]2[Mo8O26]·2DMF

A novel β-octamolybdate supported complex [Ba(DMF)₂(H₂O)]₂[Mo₈O₂₆]·2DMF (1) was synthesized by the direct modification to the surface of octamolybdate molecular cluster. Its structure was determined by elemental analysis, TG analysis, IR spectrum, and the single-crystal X-ray diffraction. The title compound crystallizes in triclinic system, space group , a=9.984(2) Å, b=11.117(2) Å, c=12.681(3) Å, α=115.86(3)°, β=97.66(3)°, γ=98.11(3)°, V=1223.5(4) Å³, Z=2, λ(MoKα)=0.71073 Å, (R(F)=0.0386 for 5535 reflections). Data were collected on a Rigaku R-AXIS RAPID IP diffractometer at 293 K in the range of 2.04<θ<27.47°. Compound 1 exhibits a novel two-dimensional (2D) layered framework in which all β-[Mo₈O₂₆]⁴⁻ subunits are connected together through Ba-O-Ba-O-Mo and Ba-O-Mo bridges. Furthermore, these 2D layers are extended into 3D supramolecular network containing parallelogram channels via hydrogen-bonding interactions.     

Synthesis and characterization of organic-inorganic hybrid compounds with a pillared layer structure: Ga2(4,4′-bpy)(XO4)2 (X=P, As)

Two organic-inorganic hybrid compounds, Ga₂(4,4′-bpy)(PO₄)₂, 1, and Ga₂(4,4′-bpy)(AsO₄)₂, 2, have been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction. The two compounds are isostructural and crystallize in the triclinic space group (No. 2) with a=4.9723(9) Å, b=5.770(1) Å, c=11.812(2) Å, α=78.268(3)°, β=89.159(3)° γ=88.344(3)°, V=331.7(2) Å³, Z=1, and R1=0.0377 for 1, and a=5.1111(7) Å, b=5.9327(8) Å, c=11.788(2) Å, α=79.497(2)°, β=88.870(2)°, γ=88.784(2)°, V=351.3(2) Å³, and R1=0.0264 for 2. The structure consists of neutral sheets of GaXO₄ (X=P or As) which are pillared through 4,4′-bipyridine ligands. Each oxide layer, which is formed only by four-membered rings, is constructed from corner-sharing GaO₄N trigonal bipyramids and XO₄ tetrahedra. The title compounds are two of the few examples in which the gallium atoms are exclusively five-coordinate.     

The extended chain compounds Ln12(C2)3I17 (Ln=Pr, Nd, Gd, Dy): Synthesis, structure and physical properties

The title compounds are obtained in high yield from stoichiometric mixtures of Ln, LnI₃ and graphite, heated at 900-950 °C in welded Ta containers. The crystal structures of new Pr and Nd phases determined by single-crystal X-ray diffraction are related to those of other Ln₁₂(C₂)₃I₁₇-type compounds (C 2/c, a=19.610(1) and 19.574(4) Å, b=12.406(2) and 12.393(3) Å, c=19.062(5) and 19.003(5) Å, β=90.45(3)° and 90.41(3)°, for Pr₁₂(C₂)₃I₁₇ and Nd₁₂(C₂)₃I₁₇, respectively). All compounds contain infinite zigzag chains of C₂-centered metal atom octahedra condensed by edge-sharing into the [tcc]_∞ sequence (c=cis, t=trans) and surrounded by edge-bridging iodine atoms as well as by apical iodine atoms that bridge between chains. The polycrystalline Gd₁₂(C₂)₃I₁₇ sample exhibits semiconducting thermal behavior which is consistent with an ionic formulation (Ln³⁺)₁₂(C₂^6-)₃(I⁻)₁₇(e⁻) under the assumption that one extra electron is localized in metal-metal bonding. The magnetization measurements on Nd₁₂(C₂)₃I₁₇, Gd₁₂(C₂)₃I₁₇ and Dy₁₂(C₂)₃I₁₇ indicate the coexistence of competing magnetic interactions leading to spin freezing at T_f=5 K for the Gd phase. The Nd and Dy compounds order antiferromagnetically at T_N=25 and 29 K, respectively. For Dy₁₂(C₂)₃I₁₇, a metamagnetic transition is observed at a critical magnetic field H≈25 kOe.