Open-framework Metal Phosphates Research Articles

The proton conduction behavior of two 1D open-framework metal phosphates with similar crystal structures and different hydrogen bond networks.

Two open-framework zinc phosphates [C3N2H12][Zn(HPO4)2] (1) and [C6N4H22]0.5[Zn(HPO4)2] (2) were synthesized via hydrothermal reaction and characterized by powder X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. Both compounds have a similar crystal structure and macroscopic morphology. However, the difference in equilibrium cations, in which the propylene diamine is for 1 and the triethylenetetramine is for 2, results in a significant distinction in the dense hydrogen grid. The diprotonated propylene diamine molecule in 1 is more favorable for forming a hydrogen-bond network in three dimensions than in 2, in which the twisted triethylenetetramine forms a hydrogen bond grid with the inorganic framework only in two dimensions owing to its large steric effect. This distinction further leads to a disparity in the proton conductivity of both compounds. The proton conductivity of 1 can reach 1.00 × 10-3 S cm-1 under ambient conditions (303 K and 75% RH) and then increase to 1.11 × 10-2 S cm-1 at 333 K and 99% RH, which is the highest value among the open-framework metal phosphate proton conductors operated in the same conduction. In contrast, the proton conductivity of 2 is four orders of magnitude smaller than 1 at 303 K and 75% RH and two orders smaller than 1 at 333 K and 99% RH.

Tuning proton conduction by different particle sizes in open-framework metal phosphates

The proton conductions of open-framework metal phosphates K2[(VO)2(HPO4)2(C2O4)] (KVPC) with large and small particle sizes, namely KVPC-L and KVPC-S, have been evaluated. Varied particle sizes result in different proton conductive behaviors. KVPC-S exhibits a high proton conductivity of 1.15 × 10−2 S cm−1 under 40 °C, 95% RH and possesses a stable proton conduction for 4 h. Furthermore, proton conductivities of composite membranes are investigated, and the value can reach up to 1.19 × 10-3 S cm−1 under 60 °C, 95% RH and remain no significant change within 6 h.

A facile and efficient method to improve the proton conductivity of open-framework metal phosphates under aqueous condition

Herein, the K+ ions were doped into the inorganic layer of two 2D layer metal phosphates (C2H10N2)[Mn2(PO4)2].2H2O (1) and (C2H10N2)[Mn2(HPO4)3](H2O) (2), respectively, via ion exchange method. The resultant compounds maintained the original structures of 1 and 2, but significantly improved their proton conductivity, for example, the proton conductivity of 1 increased from 1.14 × 10−5 S.cm−1 to 3.39 × 10−2 S.cm−1 at 99% RH and 293 K after doped 0.55 K+ ions; the proton conductivity of 2 is 0.70 × 10−2 S.cm−1 at 99% RH and 293 K after doped 0.32 K+ ions, and is 4.3 times that of the orginal sample. Such a substantial increase in proton conductivity could be attributable to that the K+ ions in aqueous solutions create stronger electrostatic fields to accommodate water, and thus make a more dense and extensive hydrogen-bonding network to enhance the transport of protons.

Titanium Phosphite Ti2(HPO3)3, a New Negative Electrode Material for Lithium Ion Batteries

Research in the area of solids open-framework metal phosphates, has been experiencing considerable growth over the past two decades. Since 1980s, a series of transition metal phosphates with three-dimensional structure have been investigated. More recently, it has been revealed that the phosphite group, could also be of great interest, because of its tendency to form new solids open framework structure. In the literature, mixed-phosphite metal compounds have been widely synthesized with a variety of cations going from alkali metals to group IIIA of the periodic table. Some rare earth based phosphites have been also isolated. However, to the best of our knowledge, no compound with titanium and phosphite group has been reported. This compound has an interesting structure allowing it to be used as insertion material for electrodes of Li-ion batteries, while only phosphates and phosphides compounds have been used as electrode materials. Recently, two inorganic phosphite materials were tested as electrodes for energy storage systems and have shown very small specific capacities toward lithium insertion [1,2]. Besides, both works dealt with the use of phosphite based-compound as positive electrode. In this study, we are presenting a new titanium phosphite compound used as negative electrode material for lithium ion batteries. Ti2(HPO3)3 has been prepared under hydrothermal conditions and autogenous pressure. The structure of titanium phosphite with the determined crystallographic formula Ti2(HPO3)3 was solved in hexagonal system in centrosymmetric P63/m space group from single crystal diffraction data. The structure was solved by the direct method using, refined by full matrix least square.It has a three dimensional structure with tunnels along a- and b-axes (see figure). This is exactly what interests us to test it as an insertion electrode material. This compound displays a high thermal stability limit showed by TGA analysis. Structural and chemical characterization have been realized by XRD, IR and Raman spectroscopies respectively. Electrochemical analyses were done by galvanostatic cycling and cyclic voltammetry. On the initial discharge of cell, the Ti2(HPO3)3 electrode delivers a capacity of 740 mAh/g. In the aim of enhancing the electrochemical performances, Ti2(HPO3)3/graphene composite was also prepared via hydrothermal route. Results of both compounds will be presented and compared in this present publication. [1] U. Chung, J.L. Mesa, J.L. Pizarro, I. de Meatza, M. Bengoechea, J. Rodríguez Fernandez, M. I. Arriortua, and T. Rojo, J. Chem. Mater. 23 (2011) 4317-4330. [2] H. Yaghoobnejad Asl, K. Ghosh, M. P. Vidal Meza, A. Choudhurya, J. The Royal Society of Chemistry. (2013), 00, 1-3. Figure 1

Ionothermal synthesis of open-framework metal phosphates with a Kagomé lattice network exhibiting canted anti-ferromagnetism†Electronic supplementary information (ESI) available: Cif files, atomic parameters, X-ray diffraction patterns, IR spectra, TG curves, and thermal ellipsoid plot and atomic label schemes of compound 1-4. See DOI: 10.1039/c4tc00290cClick here for additional data file.

Four open-framework transition-metal phosphates; (NH4)2Co3(HPO4)2F4 (1), (NH4)Co3(HPO4)2(H2PO4)F2 (2), KCo3(HPO4)2(H2PO4)F2 (3), and KFe3(HPO4)2(H2PO4)F2 (4); are prepared by ionothermal synthesis using pyridinium hexafluorophosphate as the ionic liquid. Single-crystal X-ray diffraction analyses reveal that the four compounds contain cobalt/iron-oxygen/fluoride layers with Kagomé topology composed of interlinked face-sharing MO3F3/MO4F2 octahedra. PO3OH pseudo-tetrahedral groups augment the [M3O6F4] (1)/[M3O8F2] layers on both sides to give M3(HPO4)2F4 (1) and M3(HPO4)2F2 (2-4) layers. These layers are stacked along the a axis in a sequence AA…, resulting in the formation of a layer structure for (NH4)2Co3(HPO4)2F4(1). In NH4Co3(HPO4)2(H2PO4)F2 and KM3(HPO4)2(H2PO4)F2, the M3(HPO4)2F2 layers are stacked along the a axis in a sequence AA i … and are connected by [PO3(OH)] tetrahedra, giving rise to a 3-D open framework structure with 10-ring channels along the [001] direction. The negative charges of the inorganic framework are balanced by K+/NH4+ ions located within the channels. The magnetic transition metal cations themselves form layers with stair-case Kagomé topology. Magnetic susceptibility and magnetization measurements reveal that all four compounds exhibit a canted anti-ferromagnetic ground state (Tc = 10 or 13 K for Co and Tc = 27 K for Fe) with different canting angles. The full orbital moment is observed for both Co2+ and Fe2+.

Metal Complexes of Organophosphate Esters and Open-Framework Metal Phosphates: Synthesis, Structure, Transformations, and Applications

Metal Complexes of Organophosphate Esters and Open-Framework Metal Phosphates: Synthesis, Structure, Transformations, and Applications

Na[H2TETA]0.5 [ZnPO4]2×0.5H2O or TJPU‐1: A New Zincophosphate Open‐Structure Co‐Templated by Sodium and Organoamine.

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Na[H2TETA]0.5[ZnPO4]2·0.5H2O or TJPU-1: A New Zincophosphate Open-structure Co-templated by Sodium and Organoamine

Synthetic open-structured materials attract increasing attention for wide applications in catalysis, ion-exchange or intercalation. Metal phosphates are possibly the fastest expanding group of open-framework inorganic materials in the past decade. The structural diversity that stemmed from the variable coordination number and oxidation states has directed to the extensive expansion of open-framework metal phosphates. Since the bivalent metal phosphates (+2, +5) are associated with the same total charge as aluminosilicate zeolites (+3, +4), phosphate-based framework structures containing bivalent metals are considerably pursued. After the discovery of the first open-framework zincophosphate with zeolite topologies reported by G. D. Stucky, a great deal of effort has been devoted to isolating novel open-structures within this system. And this compound group has experienced extraordinary expansion in terms of the diversity of their structures and compositions. Zincophosphates with zero-, one-, two-, and three-dimensional architectures have been isolated, in which an eye-catching result is the gigantic pore structure with 24-membered rings in ND-1. This variety was achieved by varying a number of factors that can influence the structure, including template, pH, solvent, reaction temperature, additives, zinc source and others. On the other hand, the pursuit of chiral molecular sieves is of great interest with respect to the applications in enantioselective separation and syntheses. However, only a few inorganic chiral frameworks were known up to now. For the syntheses of open-structured crystals, both alkali cations and organoamine are used as structure directing reagent separately in the literatures. Although there are some compound containing both of them, systematically investigation of the co-template effect of alkali cations and organoamines is seldom. Our group has focused on metal phosphate open-structures for many years. Recently, we are interest in exploring new open-framework metal phosphates co-templated by alkali cation and organoamine. This approach has successfully yielded a new zincophosphate openstructure, Na[H2TETA]0.5[ZnPO4]2·0.5H2O (TETA = triethylenetetraamine) or TJPU-1 (TJPU = Tianjin Polytechnic University), with the zeolite CZP topology. This compound contains left-handed chiral channels along its c axis. Here we report its synthesis and crystal structure. Experimental Section

Organically Templated Vanadyl Selenites with Layered Structures.

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Understanding the building-up process of three dimensional open-framework metal phosphates: acid degradation of the 3D structures to lower dimensional structures.

Acid degradation of 3D zinc phosphates primarily yields a one-dimensional ladder compound, an observation that is significant considering that the latter forms 3D structures on heating in water.

Organically templated vanadyl selenites with layered structures.

Two layered vanadyl selenites with the compositions, [DABCOH2]0.5[(VIVO)(HSeO3)(SeO3)].H2O,I, and [enH2][(VivO)2-(VVO)O2(SeO3)3]-.1.25H2O, II, have been prepared by the reaction of NaVO3 with SeO2 or H2SeO4 under hydrothermal conditions in the presence of organic amines. Crystal data: I, orthorhombic, space group Pbcn (No. 60), a = 6.3152(3) A, b = 18.1918(8) A, c = 17.7172(8) A, V = 2035.4(2) A3, Z = 8, R1 (all data) = 0.0368; II, triclinic, space group P1 (No.2), a = 6.3406(2) A, b = 10.2085(3) A, c = 13.2551(10) A, alpha = 101.238(2) degrees, beta = 96.503(2) degrees, gamma = 104.332(2) degrees, V = 803.47(4) A3, Z = 2, R1 (all data) = 0.0814. While I contains the ladder motif, commonly found in open-framework metal phosphates, II is formed by a secondary building unit composed of a V4O18 cluster along with SeO3 and VO5 groups. The study demonstrates that the selenite unit can be fruitfully exploited to design interesting open-framework structures.

Direct synthesis of bis( n-alkylammonium) monohydrogen phosphates by solid–vapour reaction

n-Alkylamines ( C n H 2n+1 NH 2, n=2–6) have been intercalated into orthophosphoric acid by exposing the solid to the vapour of the amines. Compounds were obtained of both the (C n H 2 n+1 NH 3)(H 2PO 4) and (C n H 2 n+1 NH 3) 2(HPO 4)·H 2O formulae. In the novel monohydrogen phosphates, n-alkylamines form a bimolecular film inclined an average of 42.6° with respect to the phosphate layer plane. These compounds are proposed as starting materials for the hydrothermal synthesis of new open-framework metal phosphates.

A new route for the synthesis of open-framework metal phosphates using organophosphates

Use of tributylphosphate, an organophosphate, as the phosphorus source in place of phosphoric acid, has enabled the synthesis of several new open-framework zinc(II) and cobalt(II) phosphates, under solvothermal conditions.

Basic building units, self-assembly and crystallization in the formation of complex inorganic open architectures

Careful investigations of open-framework metal phosphates reveal that the formation of these complex architectures is likely to involve a process wherein one-dimensional ladders or chains, and possibly zero-dimensional monomers, transform to higher dimensional structures. The one-dimensional ladder appears to be the primary building unit of these structures. At one stage of the building-up process, spontaneous self-assembly of a low-dimensional structure such as the ladder seems to occur, followed by crystallization of a two-or three-dimensional structure. Accordingly, many of the higher dimensional structures retain the structural features of the 1D structure, indicating the occurrence of self-assembly. These findings mark the beginnings of our understanding of complex supramolecular inorganic materials.

Synthons and design in metal phosphates and oxalates with open architectures.

We briefly describe the structures of open-framework metal phosphates with different dimensionalities, such as the one-dimensional linear-chain and ladder structures, two-dimensional layer structures and three-dimensional structures with channels. We demonstrate the role of the zero-dimensional four-membered ring monomer and of the one-dimensional ladder structure as the starting building units or synthons involved in the formation of the complex architectures. Thus, we show how the one-dimensional ladder structure transforms to two- and three-dimensional structures under mild conditions. The two-dimensional layer structures also transform to three-dimensional structures, while the zero-dimensional monomer transforms to layered and three-dimensional structures under ordinary reaction conditions. These transformations provide an insight into the possible pathways involved in the building up of the complex structures of metal phosphates. The isolation of amine phosphates during the hydrothermal synthesis of metal phosphates and also the facile reactions between amine phosphates and metal ions to yield a variety of open-framework materials have thrown light on the mechanism of formation and design of these structures. The existence of a hierarchy of open-framework metal oxalates and their ready formation by employing amine oxalates as intermediates provides additional support to the observations made earlier with regard to the phosphates.

Aufbau principle of complex open-framework structures of metal phosphates with different dimensionalities.

Open-framework metal phosphates occur as one-dimensional (1D) chains or ladders, two-dimensional (2D) layers, and complex three-dimensional (3D) structures. Zero-dimensional monomers have also been isolated recently. These materials are traditionally prepared by hydrothermal means, in the presence of organic amines, but the reactions of amine phosphates with metal ions provide a facile route for the synthesis, and also throw some light on the mode of formation of these fascinating architectures. Careful studies of the transformations of monophasic zinc phosphates of well-characterized structures show that the 1D structures transform to 2D and 3D structures, while the 2D structures transform to 3D structures. The zero-dimensional monomers transform to 1D, 2D, and 3D structures. There is reason to believe that the 0D monomers, comprising four-membered rings, are the most basic structural units of the open-framework phosphates and that after an optimal precursor state, such as the ladder structure, is formed, further building may occur spontaneously. Evidence for the occurrence of self-assembly in the formation of complex structures is provided by the presence of the structural features of the one-dimensional starting material in the final products. These observations constitute the beginning of our understanding of the building-up principle of such complex structures.

Building Open-Framework Metal Phosphates from Amine Phosphates and a Monomeric Four-Membered Ring Phosphate

Several amine phosphates have been synthesized and their structures elucidated by single crystal X-ray diffraction. The amine phosphates, on reaction with metal ions, give rise to a large variety of metal phosphate structures incorporating the amine molecules, thus providing a facile route to the open-framework materials. By means of such a soft chemical method, it has been possible to generate novel architectures, typical of these being a cloverite structure, a new chlorophosphate incorporating chlorine as part of the framework, and a four-membered ring monomeric phosphate. The studies indicate that amine phosphates are likely to act as intermediates in the formation of open-framework metal phosphates. The transformation of the monomeric zinc phosphate to an open-framework layered structure on heating it in water suggests the four-membered ring to be the basic building unit.

Exploration of a Simple Universal Route to the Myriad of Open-Framework Metal Phosphates

The reaction of a single amine phosphate, piperazine phosphate, with ZnII ions is shown to yield a variety of open-framework metal phosphate structures. It is noteworthy that the reaction of this amine phosphate with ZnII ions yields a hierarchy of structures, including the linear chain, layer and 3-dimensional systems. Of particular interest is the isolation of the linear chain structure consisting of corner-shared four-membered rings, which has been considered to be the primary building block. By the reaction of piperazine phosphate with CoII ions, we obtained a new strip and a layer structure. Reaction of piperazine phosphate with SnII yields a layer structure. The significant role of the amine phosphates in the formation of open-framework metal phosphate structures is also supported by the isolation of a monomeric four-membered zinc phosphate, which on heating transforms to an open-framework structure.

Simple linear-chain cobalt phosphates

Two simple one-dimensional cobalt phosphates containing linear chains of corner-shared 4-membered rings have been synthesized hydrothermally by the reaction between amine phosphates and cobalt(II) ions under non-aqueous conditions. The linear chains are held together by hydrogen bond interactions involving the hydrogens of the amine and the framework oxygens. The two cobalt phosphates reported are the first linear chain compounds discovered in the family of open-framework transition metal phosphates.