We report the synthesis, structural characterization, and functionality (framework interconversions together with proton conductivity) of an open-framework hybrid that combines Ca(2+) ions and the rigid polyfunctional ligand 5-(dihydroxyphosphoryl)isophthalic acid (PiPhtA). Ca2[(HO3PC6H3COOH)2]2[(HO3PC6H3(COO)2H)(H2O)2]·5H2O (Ca-PiPhtA-I) is obtained by slow crystallization at ambient conditions from acidic (pH ≈ 3) aqueous solutions. It possesses a high water content (both Ca coordinated and in the lattice), and importantly, it exhibits water-filled 1D channels. At 75 °C, Ca-PiPhtA-I is partially dehydrated and exhibits a crystalline diffraction pattern that can be indexed in a monoclinic cell with parameters close to the pristine phase. Rietveld refinement was carried out for the sample heated at 75 °C, Ca-PiPhtA-II, using synchrotron powder X-ray diffraction data, which revealed the molecular formula Ca2[(HO3PC6H3COOH)2]2[(HO3PC6H3(COO)2H)(H2O)2]. All connectivity modes of the "parent" Ca-PiPhtA-I framework are retained in Ca-PiPhtA-II. Upon Ca-PiPhtA-I exposure to ammonia vapors (28% aqueous NH3) a new derivative is obtained (Ca-PiPhtA-NH3) containing 7 NH3 and 16 H2O molecules according to elemental and thermal analyses. Ca-PiPhtA-NH3 exhibits a complex X-ray diffraction pattern with peaks at 15.3 and 13.0 Å that suggest partial breaking and transformation of the parent pillared structure. Although detailed structural identification of Ca-PiPhtA-NH3 was not possible, due in part to nonequilibrium adsorption conditions and the lack of crystallinity, FT-IR spectra and DTA-TG analysis indicate profound structural changes compared to the pristine Ca-PiPhtA-I. At 98% RH and T = 24 °C, proton conductivity, σ, for Ca-PiPhtA-I is 5.7 × 10(-4) S·cm(-1). It increases to 1.3 × 10(-3) S·cm(-1) upon activation by preheating the sample at 40 °C for 2 h followed by water equilibration at room temperature under controlled conditions. Ca-PiPhtA-NH3 exhibits the highest proton conductivity, 6.6 × 10(-3) S·cm(-1), measured at 98% RH and T = 24 °C. Activation energies (Ea) for proton transfer in the above-mentioned frameworks range between 0.23 and 0.4 eV, typical of a Grothuss mechanism of proton conduction. These results underline the importance of internal H-bonding networks that, in turn, determine conductivity properties of hybrid materials. It is highlighted that new proton transfer pathways may be created by means of cavity "derivatization" with selected guest molecules resulting in improved proton conductivity.

The chemistry of metal phosphonates has been progressing fast with the addition of new materials that possess novel structural features and new properties, occasionally in a cooperative manner. In this paper, we report a new family of functional lanthanide-carboxyphosphonate materials. Specifically, the lanthanide is La, Ce, Pr, Sm, Eu, Gd, Tb, or Dy and the carboxyphosphonate ligand is 2-hydroxyphosphonoacetic acid ( H 3 H P A ) . A l l r e p o r t e d L n H P A c o m p o u n d s , Ln 3 (H 0.75 O 3 PCHOHCOO) 4 •xH 2 O (x = 15−16), crystallize in the orthorhombic system. Two types of structures were isolated: series I and II polymorphs. For both series, the three-dimensional (3D) open frameworks result from the linkage of similar organo-inorganic layers, in the ac-plane, by central lanthanide cations, which yield trimeric units also found in other metal-HPA hybrids. Large oval-shaped 1D channels are formed by the spatial separation of the layers along the b-axis and filled with lattice water molecules. LnHPA materials undergo remarkable crystalline-to-amorphous-to crystalline transformations upon dehydration and rehydration cycles, as confirmed by thermodiffraction and NMR spectroscopy. The highest proton conductivity was observed for GdHPA (series II), 3.2 × 10 −4 S cm −1 at 98% RH and T = 21°C. The dehydration−rehydration chemistry was also followed by photoluminescence spectroscopy. It was shown that loss and reuptake of water molecules are accompanied by clear changes in the photoluminescence spectra and lifetimes of the Eu analog (series II). Our present results reveal a wide family of wellcharacterized, multifunctional lanthanide-based phosphonate 3D-structured metal−organic frameworks (MOFs) that show reversible crystalline-to-amorphous-to-crystalline transformations and, at the same time, exhibit high proton conductivity.

Multifunctional materials, especially those combining two or more properties of interest, are attracting immense attention due to their potential applications. MOFs, metal organic frameworks, can be regarded as multifunctional materials if they show another useful property in addition to the adsorption behavior. Here, we report a new multifunctional light hybrid, MgH(6)ODTMP·2H(2)O(DMF)(0.5) (1), which has been synthesized using the tetraphosphonic acid H(8)ODTMP, octamethylenediamine-N,N,N',N'-tetrakis(methylenephosphonic acid), by high-throughput methodology. Its crystal structure, solved by Patterson-function direct methods from synchrotron powder X-ray diffraction, was characterized by a 3D pillared open framework containing cross-linked 1D channels filled with water and DMF. Upon H(2)O and DMF removal and subsequent rehydration, MgH(6)ODTMP·2H(2)O (2) and MgH(6)ODTMP·6H(2)O (3) can be formed. These processes take place through crystalline-quasi-amorphous-crystalline transformations, during which the integrity of the framework is maintained. A water adsorption study, at constant temperature, showed that this magnesium tetraphosphonate hybrid reversibly equilibrates its lattice water content as a function of the water partial pressure. Combination of the structural study and gas adsorption characterization (N(2), CO(2), and CH(4)) indicates an ultramicroporous framework. High-pressure CO(2) adsorption data are also reported. Finally, impedance data indicates that 3 has high proton conductivity σ = 1.6 × 10(-3) S cm(-1) at T = 292 K at ~100% relative humidity with an activation energy of 0.31 eV.

This article reviews the synthesis, characterization and ion-exchange, ion-transport, sorptive, and catalytic properties of inorganically pillared layered metal(IV) phosphates, typified by Zr(HPO 4 ) 2 ‚H 2 O. Porous nanostructures are generally prepared from metal(IV) phosphates either by ion exchange of polynuclear species or by intercalation from solutions of condensed species obtained by the hydrolysis of organometallic precursors using sol-gel methods, followed by thermal treatment to eliminate organic moieties, condense hydroxyl groups, eliminate water, and consolidate the structure by grafting the pillar to the layer. The different strategies devised to overcome the problem presented by the high layer charge density of R-and γ-structured phosphates in obtaining porous solids, including exfoliation and local surface growth of pillaring ions, and modification of the zirconium phosphate matrix to reduce the cation-exchange capacity, are described. Structural and textural characteristics of Al, Cr, mixed Al-Cr, Fe-Cr, Ga-Al and of Si-pillared phosphates obtained from XAFS, XPS, and MAS NMR are presented, and the perspectives of nanocomposite pillared layered solids in general are discussed in the current context of mesoporous solids synthesized using templating routes.

The continuous demand for acidic solids for use in the fields of catalysis and sorption has greatly encouraged the search for new materials with a porosity and intrinsic reactivity that can be tailored. [1] The synthesis of the family of M41S solids has shown that surfactant species favor, by a mechanism of cooperative nucleation, the formation of organo-inorganic nanocomposite biphase arrays, the structures of which mimic those of liquid crystals. [2,3] This synthetic approach is demonstrating its importance by its versatility, and a great variety of mesoporous solids have been prepared since the landmark articles of Beck et al. We report here the sol-gel synthesis of zirconium phosphate in the presence of a structure-directing cationic surfactant, leading to mesoporous solids with a BET (Brunauer±Em-mett±Teller) surface area of ca. 250±320 m 2 g ±1 and a high and modulable surface acidity following removal of the surfactant by acid±ethanol extraction or by calcination at 540 C.Zirconium phosphate is the most studied member of the well-known family of layered solid acids. [4] ªPillaredº derivatives can be prepared by intercalation of inorganic or organometallic species followed by a grafting reaction designed to eliminate organic matter, dehydroxylate, and anchor the pillaring metal oxide nanoparticle formed to the layer. These multifunctional zeolite-like compounds are meso-and microporous, and have potential applications as catalysts and catalyst supports. [5] Although templated syntheses of open-framework phosphates has been developed as a route to ultra-large pore solids, [6] until very recently, surfactant-assisted syntheses of metal phosphates led only to layered phases, [7] and the synthesis of mesoporous phosphate-based solids with pore dimensions larger than those of the aluminum phosphates remained a challenge. Last year, however, Zhao et al. reported the preparation of a thermally stable mesoporous hexagonal aluminophosphate and silicoaluminophosphate with BET surface areas of 772 and 928 m 2 g ±1 , respectively. [8] Some months earlier, Ciesla et al. had recourse to phosphoric acid treatment of a surfactant-containing zirconium oxosulfate gel, which, by neutralizing the remaining ZrOH groups, helped to avoid the structural collapse of the zirconium oxide on removal of the surfactant. This led to high surface area zirconium oxophosphate. [9] In a different approach, we have used phosphoric acid directly at the stage of the formation of the inorganic matrix, and now report the templated synthesis and characterization of a new mesoporous zirconium phosphate with uniform pore dimensions and acidic properties.The synthesis of this new templated zirconium phosphate (t-ZrP) was carried out by mixing an aqueous solution of cetyltrimethylammonium (CTMA) bromide (25 wt.-%, Aldrich) with orthophosphoric acid (85 wt.-%, BDH Analar) (P/CTMA molar ratio = 1). The CTMA solution was then aged for at least 30 min before adding zirconium n-propoxide (Zr(OC 3 H 7 ) 4 , 70 wt.-% solution in 1-propanol, Aldrich), in...