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Analogous to 2D layered transition-metal dichalcogenides, the TlSe family of quasi-one dimensional chain materials with the Zintl-type structure exhibits novel phenomena under high pressure. In the present work, we have systematically investigated the high-pressure behavior of TlInTe2 using Raman spectroscopy, synchrotron X-ray diffraction (XRD), and transport measurements, in combination with first principles crystal structure prediction (CSP) based on evolutionary approach. We found that TlInTe2 undergoes a pressure-induced semiconductor-to-semimetal transition at 4 GPa, followed by a superconducting transition at 5.7 GPa (with Tc = 3.8 K). An unusual giant phonon mode (Ag) softening appears at ∼10-12 GPa as a result of the interaction of optical phonons with the conduction electrons. The high-pressure XRD and Raman spectroscopy studies reveal that there is no structural phase transitions observed up to the maximum pressure achieved (33.5 GPa), which is in agreement with our CSP calculations. In addition, our calculations predict two high-pressure phases above 35 GPa following the phase transition sequence as I4/mcm (B37) → Pbcm → Pm3m (B2). Electronic structure calculations suggest Lifshitz (L1 & L2-type) transitions near the superconducting transition pressure. Our findings on TlInTe2 open up a new avenue to study unexplored high-pressure novel phenomena in TlSe family induced by Lifshitz transition (electronic driven), giant phonon softening, and electron-phonon coupling.

We report a synthetic pathway by which amorphous Al(OH)3 is converted to γ-AlOOH through hydrothermal reaction in the presence of water at temperature T ​= ​473 ​K. X-ray pair distribution function measurements reveal that the initially amorphous Al(OH)3 possesses a locally γ-Al(OH)3-like structure, while nanocrystalline γ-AlOOH precipitates within 1 ​h of continuous hydrothermal exposure. Solid state nuclear magnetic resonance measurements show that resonant features associated with four- and five-member Al clusters persist through 20 ​min of hydrothermal treatment, and ultraviolet (UV) spectra mark the onset of UV-induced photoluminescent features characteristic to γ-AlOOH with 10 ​min of exposure, indicating a coexistence region of γ-Al(OH)3-like and γ-AlOOH-like amorphous species. Powder x-ray diffraction measurements of desiccated powders reveal that the conversion process takes place in distinct, power law-defined stages with initial γ-AlOOH nucleation occurring within the first 20 ​min, followed by a ~ 1 ​h period of rapid grain coarsening and the subsequent onset of Lifshitz-Slyozov-Wagner-like coalescence.

Cu/CHA catalysts with various Cu loadings (0.5 wt%–6.0 wt%) were synthesized via incipient wetness impregnation. The catalysts were applied to the selective catalytic reduction (SCR) of NO with NH3 and NO oxidation reaction. XRD and N2 adsorption-desorption data showed that CHA structure was maintained with the incorporation of Cu, while specific surface areas decreased with increasing Cu loading. At intermediate Cu loading, 4 wt%, the highest NH3-SCR activity was observed with ∼98% N2 selectivity from 150 °C to 300 °C. Small amounts of water, 2%, slightly increased NO conversion in addition to the remarkable N2O and NO2 reduction at high temperature. Water effects are attributed to the improved Cu ion reducibility and mobility. NO oxidation results provided no relation between NO2 formation and SCR activity. Physicochemical properties, NO conversion, N2 selectivity, and activation energy data showed that impregnated samples’ molecular structure and catalytic activity are comparable to the conventional ion-exchanged (IE) samples’ ones.

Different structural phases (e.g., TT, T, and H) of niobium oxide were synthesized, characterized by XRD and Raman, and utilized for the furfuryl alcohol dehydration and condensation under mild conditions (100 °C and ambient pressure). Furfuryl alcohol conversion was dependent on reaction time and niobium oxide phase. Niobic acid and T/H phase transitional niobium oxide showed higher catalytic activity in comparison to a single crystalline phase niobium oxide. While T/H phase transitional niobium oxide showed higher conversion than that of niobic acid and TT phase niobium oxide, higher C 9 -C 15 products' selectivity (> 60%) was obtained with the latter catalysts.

High energy X-ray diffraction has been combined with containerless techniques to determine the structure of a series of alkali and ammonium nitrate and nitrite liquids. The systems have been modelled using molecular dynamics simulation which allows for the flexibility of, and movement of charge within, the molecular anions. The model reproduces the experimentally-determined scattering functions in both the low- and high-Q regimes reflecting the inter- and intra-molecular length-scales. For ammonium nitrate the best fit to the diffraction data is obtained by assuming the NH4+ cation to have a radius closer to that for Cs+ rather than a smaller cation such as Rb+ as often previously assumed. The alkali nitrites show an emergent length scale, attributed to the nitrogen-nitrogen spatial correlations, that depends on both temperature and the identity of the alkali cation. The corresponding nitrates show a more subtle effect in the nitrogen-nitrogen correlations. As a result, the nature of this N-N length-scale appears different for the respective nitrites and nitrates.

Gate-opening is a unique and interesting phenomenon commonly observed in flexible porous frameworks, where the pore characteristics and/or crystal structures change in response to external stimuli such as adding or removing guest molecules. For gate-opening that is induced by gas adsorption, the pore-opening pressure often varies for different adsorbate molecules and, thus, can be applied to selectively separate a gas mixture. The detailed understanding of this phenomenon is of fundamental importance to the design of industrially applicable gas-selective sorbents, which remains under investigated due to the lack of direct structural evidence for such systems. We report a mechanistic study of gas-induced gate-opening process of a microporous metal-organic framework, [Mn(ina)2 ] (ina=isonicotinate) associated with commensurate adsorption, by a combination of several analytical techniques including single crystal X-ray diffraction, in situ powder X-ray diffraction coupled with differential scanning calorimetry (XRD-DSC), and gas adsorption-desorption methods. Our study reveals that the pronounced and reversible gate opening/closing phenomena observed in [Mn(ina)2 ] are coupled with a structural transition that involves rotation of the organic linker molecules as a result of interaction of the framework with adsorbed gas molecules including carbon dioxide and propane. The onset pressure to open the gate correlates with the extent of such interaction.

The adsorption mechanism of ethane, ethylene, and acetylene (C2Hn; n = 2, 4, 6) on two microporous metal organic frameworks (MOFs) is described here that is consistent with observations from single crystal and powder X-ray diffraction, calorimetric measurements, and gas adsorption isotherm measurements. Two calcium-based MOFs, designated as SBMOF-1 and SBMOF-2 (SB: Stony Brook), form three-dimensional frameworks with one-dimensional open channels. As determined from single crystal diffraction experiments, channel geometries of both SBMOF-1 and SBMOF-2 provide multiple adsorption sites for hydrocarbon molecules through C–H···π and C–H···O interactions, similarly to interactions in the molecular and protein crystals. Both materials selectively adsorb C2 hydrocarbon gases over methane as determined with IAST and breakthrough calculations as well as experimental breakthrough measurements, with C2H6/CH4 selectivity as high as 74 in SBMOF-1.

A series of polystyrene-block-poly(4-(phenylethynyl)styrene) (PS-b-PPES) diblock copolymers with a range of compositions were prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization. Block copolymer/cobalt carbonyl adducts (PSx-PPESy[Co2(CO)6]n) were subsequently prepared by reaction of Co2(CO)8 with the alkyne groups of the PPES block. Phase behavior of the block copolymer/cobalt carbonyl adducts (PSx-PPESy[Co2(CO)6]n, 8% ≤ wt % PS ≤ 68%) was studied by small-angle X-ray scattering and transmission electron microscopy (TEM). As the composition of PSx-PPESy[Co2(CO)6]n copolymers was shifted from PS as the majority block to PPESy[Co2(CO)6]n as the majority block, the morphology was observed to shift from lamellar with larger PS domains to cylindrical with PS as the minority component and then to spherical with PS as the minority component. These observations have been used to map out a partial phase diagram for PSx-PPESy[Co2(CO)6]n diblock copolymers. Heating of PSx-PPESy[Co2(CO)...

The efficiency of physisorption-based separation of gas-mixtures depends on the selectivity of adsorbent which is directly linked to size, shape, polarizability and other physical properties of adsorbed molecules. Commensurate adsorption is an interesting and important adsorption phenomenon, where the adsorbed amount, location, and orientation of an adsorbate are commensurate with the crystal symmetry of the adsorbent. Understanding this phenomenon is important and beneficial as it can provide vital information about adsorbate–adsorbent interaction and adsorption–desorption mechanism. So far, only sporadic examples of commensurate adsorption have been reported in porous materials such as zeolites and metal organic frameworks (MOFs). In this work we show for the first time direct structural evidence of commensurate-to-incommensurate transition of linear hydrocarbon molecules (C2–C7) in a microporous MOF, by employing a number of analytical techniques including single crystal X-ray diffraction (SCXRD), in situ powder X-ray diffraction coupled with differential scanning calorimetry (PXRD-DSC), gas adsorption and molecular simulations.

Capture of highly volatile radioactive iodine is a promising application of metal-organic frameworks (MOFs), thanks to their high porosity with flexible chemical architecture. Specifically, strong charge-transfer binding of iodine to the framework enables efficient and selective iodine uptake as well as its long-term storage. As such, precise knowledge of the electronic structure of iodine is essential for a detailed modeling of the iodine sorption process, which will allow for rational design of iodophilic MOFs in the future. Here we probe the electronic structure of iodine in MOFs at variable iodine···framework interaction by Raman and optical absorption spectroscopy at high pressure ( P). The electronic structure of iodine in the straight channels of SBMOF-1 (Ca- sdb, sdb = 4,4'-sulfonyldibenzoate) is modified irreversibly at P3.4 GPa by charge transfer, marking a polymerization of iodine molecules into a 1D polyiodide chain. In contrast, iodine in the sinusoidal channels of SBMOF-3 (Cd- sdb) retains its molecular (I

Photocatalytic hydrogen evolution from water was observed over nanocrystalline gallium oxynitride spinel under simulated solar light irradiation (320 nm < λ < 800 nm). Up to 8 μmol h−1 of H2 was evolved without co-catalyst loading. The photocatalyst was synthesized by the ammonolysis of gallium nitrate hydrate (Ga(NO3)3·xH2O). Optical measurements indicate an indirect gap (Eg) in the visible region (Eg = 2.50 eV) which is ascribed to photoexcitations from the N 2p valence states. A direct gap has an onset at ultraviolet energies (Eg = 3.69 eV), which is ascribed to photoexcitations from lower energy O 2p valence states.

As part of an effort to characterize clusters and intermediate phases likely to be encountered along solution reaction pathways that produce iron and aluminum oxide-hydroxides from Fe and Al precursors, the complete structure of Al10O14(OH)2 (akdalaite) was determined from a combination of single-crystal X-ray diffraction (SC-XRD) data collected at 100 K to define the Al and O positions, and solid-state nuclear magnetic resonance (NMR) and neutron powder diffraction (NPD) data collected at room temperature (~300 K) to precisely determine the nature of hydrogen in the structure. Two different synthesis routes produced different crystal morphologies. Using an aluminum oxyhydroxide floc made from mixing AlCl3 and 0.48 M NaOH, the product had uniform needle morphology, while using nanocrystalline boehmite (Vista Chemical Company Catapal D alumina) as the starting material produced hexagonal plates. Akdalaite crystallizes in the space group P63mc with lattice parameters of a = 5.6244(3) &Aring, and c = 8.8417(3) &Aring, (SC-XRD) and a = 5.57610(2) &Aring, and c = 8.77247(6) &Aring, (NPD). The crystal structure features Al13O40 Keggin clusters. The structural chemistry of akdalaite is nonideal but broadly conforms to that of ferrihydrite, the nanomineral with which it is isostructural.

The influence of crystallite size on the adsorption reactivity of phosphate on 2-line to 6-line ferrihydrites was investigated by combining adsorption experiments, structure and surface analysis, and spectroscopic analysis. X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the ferrihydrite samples possessed a similar fundamental structure with a crystallite size varying from 1.6 to 4.4 nm. N2 adsorption on freeze-dried samples revealed that the specific surface area (SSABET) decreased from 427 to 234 m(2) g(-1) with increasing crystallite size and micropore volume (Vmicro) from 0.137 to 0.079 cm(3) g(-1). Proton adsorption (QH) at pH 4.5 and 0.01 M KCl ranged from 0.73 to 0.55 mmol g(-1). Phosphate adsorption capacity at pH 4.5 and 0.01 M KCl for the ferrihydrites decreased from 1690 to 980 μmol g(-1) as crystallite size increased, while the adsorption density normalized to SSABET was similar. Phosphate adsorption on the ferrihydrites exhibited similar behavior with respect to both kinetics and the adsorption mechanism. The kinetics could be divided into three successive first-order stages: relatively fast adsorption, slow adsorption, and a very slow stage. With decreasing crystallite size, ferrihydrites exhibited increasing rate constants per mass for all stages. Analysis of OH(-) release and attenuated total reflectance infrared spectroscopy (ATR-IR) and differential pair distribution function (d-PDF) results indicated that initially phosphate preferentially bound to two Fe-OH2(1/2+) groups to form a binuclear bidentate surface complex without OH(-) release, with smaller size ferrihydrites exchanging more Fe-OH2(1/2+) per mass. Subsequently, phosphate exchanged with both Fe-OH2(1/2+) and Fe-OH(1/2-) with a constant amount of OH(-) released per phosphate adsorbed. Also in this stage binuclear bidentate surface complexes were formed with a P-Fe atomic pair distance of ~3.25 Å.

A three dimensional lithium hydronium sulfate LiSO4·H3O [1], [space group Pna21 a=8.7785(12) A, b=9.1297(12) A, c=5.2799(7) A, V=423.16(10) A3] was synthesized via solvothermal methods using 1,5-naphthalenedisulfonic acid (1,5-NSA) as the source of sulfate ions. The structure of [1], determined by single crystal X-ray diffraction techniques, consists of corner sharing LiO4 and SO4 tetrahedra, forming an anionic 3-D open framework that is charge balanced by hydronium ions positioned within channels running along [001] and forming strong H-bonding with the framework oxygen atoms. Compound [1] undergoes two reversible phase transitions, involving reorientation of SO42− ions at pressures of approximately 2.5 and 5 GPa at room temperature, as evident from characteristic discontinuous frequency drops in the ν1 mode of the Raman spectra. Additionally, compound [1] forms dense β-lithium sulfate at 300 °C, as evident from temperature dependent powder XRD and combined reversible TGA-DSC experiments.

A series of three magnesium trimesate coordination networks was synthesized from identical reaction mixtures by varying synthetic temperature. Mg(HBTC)(DMF)2·[(CH3)2NH] (1; BTC = trimesate; space group P63/m, a = 16.596(4) A, c = 14.351(8) A) crystallizes at 65 °C, Mg3(BTC)(HCOO)3(DMF)3 (2; space group P ¯ 3, a = 13.928(2) A, c = 8.025(6) A) crystallizes at 100 °C, and Mg3(BTC)2(DMF)4 (3; space group P21/c, a = 17.490(4) A, b = 11.940(2) A, c = 18.460(4) A, β = 116.87(3)°) crystallizes at a temperature of 180 °C. Each network contains metal-coordinated solvent DMF molecules, but thermodynamics and solvent hydrolysis play major roles in structure formation. Compounds 1 and 2 are two-dimensional networks which incorporate hydrolysis byproducts. Compound 3 is a three-dimensional network and shows no inclusion of byproducts. The series follows the trend of increased network connectivity resulting from increased temperature. Each of the networks show a weak photoluminescence response, suggesting that coordinated solvent molecules and interlayer species play a role in quenching photoluminescence.

Three topologically-related lanthanide thiophenedicarboxylate (TDC) metal-organic frameworks were synthesized using an identical metal:linker:solvet ratio. Nd(TDC)3(EtOH)3(H2O)·H2O (1; space group Cc, a = 24.035(2) A, b = 10.063(1) A, c = 18.998(1) A, β = 132.41(1)°) contains the same metal-TDC coordination modes as two other compounds which have the isostructural formula Ln(TDC)3(EtOH)3(H2O)·H2O; Ln = Tb (2; space group P ¯ 1, a = 12.807(9) A, b = 14.557(1) A, c = 19.128(1) A, α = 106.66(2)°, β = 105.62(2)°, γ = 93.691(2)°), Dy (3; space group P ¯ 1, a = 12.793(8) A, b = 14.682(1) A, c = 19.077(1) A, α = 107.12(1)°, β = 105.54(1)°, γ = 93.518(2)°). An equimolar solvent mixture of water and ethanol causes both types of solvent molecules coordinating to metal centers. The fluorescence spectra of compounds 2 and 3 show characteristic bands related to their respective metal ions, but Dy-based 3 is very weak compared to Tb-based 2, indicating coordinating solvent molecules may be quenching Dy fluorescence.

Understanding the interactions between adsorbed gas molecules and a pore surface at molecular level is vital to exploration and attempts at rational development of gasselective nanoporous solids. Much current work focuses on the design of functionalized metal–organic frameworks (MOFs) or coordination networks (CNs) that selectively adsorb CO2. [1–9] While interactions between CO2 molecules and the p clouds of aromatic linkers in MOFs under ambient conditions have been explored theoretically, no direct structure evidence of such interactions are reported to date. Here we provide the first structural insight of such interactions in a porous calcium based CN using single-crystal X-ray diffraction methods, supported by powder diffraction coupled with differential scanning calorimetry (DSC-XRD), in situ IR/Raman spectroscopy, and molecular simulation data. We further postulate that such interactions are responsible for the high CO2/N2 adsorption selectivity, even in the case of a high relative humidity (RH). Our data suggest that the key interaction responsible for such selectivity, the room-temperature stability and the relative insensitivity to the RH of the CO2-CN adduct, is between two phenyl rings of the linker in the CN and the molecular quadrupole of CO2. The specific geometry of the linker molecule results in a “pocket” where carbon from the CO2 molecule is placed between two centroids of the aromatic ring. Our experimental confirmation of this variation on theoretically postulated interactions between CO2 and a phenyl ring will promote the search for other CNs containing phenyl ring pockets. Selective adsorption and sequestration of CO2 from sources of anthropogenic emissions, such as untreated waste from flue gas and products of the water gas shift reaction, is important to mitigate the growing level of atmospheric CO2. [10] Current separation methods use absorption in alkanolamine solutions, which are toxic, corrosive, and require significant energy for their regeneration. Hence microporous solid-state adsorbents, such as zeolites, hybrid zeolite–polymer systems, porous organic materials, and MOFs are proposed as alternatives, especially in combination with pressure swing processes. Rather than relying solely on tuning the pore diameters of microporous materials to select between gases based on size (the kinetic diameters of CO2, CH4 and N2 are 3.30, 3.76 3.64 , respectively ) selective separation relies on differences in electronic properties, such as the quadrupole moment and polarizability. Attempts to produce MOFs or CNs with adsorption properties competitive with those of commercially established aluminosilicate zeolites, relies on strategies that include pore surface modification with strongly polarizing functional groups, such as amines 7, 9,15] and desolvating metals centers 8, 16] to produce low-coordinated sites suitable for CO2 adsorption. The amine-functionalized materials offer a high selectivity toward CO2 adsorption, but a low effective surface area and thus, a low total uptake capacity. Strong interactions with polarizing functional groups, as well as with open metal sites presents other drawbacks including an increase in the costs for material regeneration. Furthermore, water effectively competes with CO2 at low-coordinated cation sites, impeding the performance of frameworks in commercial flue gas. We recently described a porous framework, CaSDB (SDB: sulfonyldibenzoate, compound 1) with a high CO2/N2 selectivity. At 0.15 bar of CO2 and 0.85 bar of N2, a typical composition of flue gas mixture from power plants, the selectivity is in the range of 48 to 85 at 298 K. CaSDB shows a reversible uptake of CO2 of 5.75 wt% at 273 K and 1 bar pressure and 4.37 wt% at room temperature, with heats of adsorption for CO2 and N2 of 31 and 19 kJmol , respectively. The as-synthesized compound contains not coordinated water molecules and is easily activated for gas adsorption by heating to 563 K in vacuum; remarkably the activated framework does not readsorb water, even if exposed to a RH greater than [*] A. M. Plonka, W. R. Woerner, Prof. Dr. J. B. Parise Department of Geosciences, Stony Brook University Stony Brook, NY 11794-2100 (USA) E-mail: john.parise@stonybrook.edu

The application of pressure in solid-state synthesis provides a route for the creation of new and exciting materials. However, the onerous nature of high-pressure techniques limits their utility in materials discovery. The systematic search for novel oxynitrides-semiconductors for photocatalytic overall water splitting-is a representative case where quench high-pressure synthesis is useful and necessary in order to obtain target compounds. We utilize state of the art crystal structure prediction theory (USPEX) and in situ synchrotron-based X-ray scattering to speed up the discovery and optimization of novel compounds using high-pressure synthesis. Using this approach, two novel oxynitride phases were discovered in the GaN-Nb2O5 system. The (Nb2O5)0.84:(NbO2)0.32:(GaN)0.82 rutile structured phase was formed at 1 GPa and 900 °C and gradually transformed to a α-PbO2-related structure above 2.8 GPa and 1000 °C. The low-pressure rutile type phase was found to have a direct optical band gap of 0.84 eV and an indirect gap of 0.51 eV.

The interaction of calcium with phosphate at mineral/water interfaces is of importance for understanding both P sequestration and phosphate mineral formation. We investigated the effect of dissolved calcium on phosphate uptake by boehmite in batch sorption studies as a function of pH. Examination of the solids by 31 P NMR spectroscopy and powder X-ray diffraction (XRD) shows evidence for formation of hydroxylapatite from pH 7 to pH 9, which is supported by correlation of Ca and P on particle surfaces at pH 9 observed by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX) analysis. At pH 6, two major 31 P NMR peaks are observed at δ P–31 = 0 and −6 ppm, indicating the presence of bidentate binuclear complexes with surface Al atoms, similar to those found in the absence of dissolved Ca. At higher pH, an additional 31 P peak at δ P–31 = 2.65 ppm is observed, consistent with hydroxylapatite (Hap). The NMR data indicate that after 30 days most of the phosphate (75%) remained as adsorption complexes at pH 7, but that Hap accounts for most of the phosphate at higher pH, although surface complexes were still evident in CP/MAS NMR spectra. The identification of crystalline Hap is further supported by 31 P{ 1 H} heteronuclear correlation (HetCor) experiments in which the 2.65 ppm 31 P peak correlates to a narrow 1 H peak at δ H–1 = 0.2 ppm that is diagnostic of the hydroxyl groups of Hap. In powder X-ray diffraction patterns, two small peaks are observed at slow scan rates that match the major reflections of Hap. Nonetheless, Hap crystals could not be identified in SEM images suggesting small particle size, in agreement with broad XRD peaks. At short reaction times only adsorbed phosphate is observed at pH 7, whereas Hap forms within 15 min at pH 9. These results indicate that the crystallization rate of Hap is enhanced by the boehmite surface, although the detailed mechanisms could not be discerned from these data.

Two new magnesium-based isophthalate coordination networks result from the variation of solvent and temperature: Mg4(IPA)3(HCOO)2(DMF)2 [1; IPA = isophthalate; space group Fdd2, a = 22.480(5) A, b = 38.210(8) A, c = 8.8690(2), V = 7618(3) A

A thermally stable, microporous calcium coordination network shows a reversible 5.75 wt % CO2 uptake at 273 K and 1 atm pressure, with an enthalpy of interaction of ∼31 kJ/mol and a CO2/N2 selectivity over 45 under ideal flue gas conditions. The absence of open metal sites in the activated material suggests a different mechanism for selectivity and high interaction energy compared to those for frameworks with open metal sites.

Evolution of concentrated Fe 2 (SO 4 ) 3 solution, a process including both evaporation of the solution and post-evaporation aging of the precipitates, was studied at 2 and 50 °C under controlled relative humidity (RH). At 50 °C and 42–47% RH, ferricopiapite [Fe 4.67 (SO 4 ) 6 (OH) 2 ·20H 2 O] and rhomboclase [(H 5 O 2 )Fe(SO 4 ) 2 ·2H 2 O] first crystallized from the starting solution, and then combined to form kornelite [Fe 2 (SO 4 ) 3 ·7.5H 2 O] at 42% RH or to paracoquimbite [Fe 2 (SO 4 ) 3 ·9H 2 O] at 46–47% RH. At 2 °C and 34–43% RH, initially crystallized ferricopiapite and rhomboclase appeared to be stable and did not proceed to form a single ferric sulfate hydrate phase over 385 days. At both 2 and 50 °C and RH ≤ 31%, an amorphous ferric sulfate formed. The amorphous ferric sulfate was preserved longer at low RH conditions, e.g., RH ≤ 11%, than higher RH, at which it slowly transformed to crystalline phases of rhomboclase and ferricopiapite, as observed at 31% RH and 50 °C. Combining the results from this study and those from our previous study at 25 °C, the ferric sulfate phase evolution at 2, 25, and 50 °C were mapped and compared. Temperature shows a strong effect on the evolution kinetics; low T may inhibit the evolution from reaching an equilibrium state. Also, an RH and T -controlled in situ X-ray diffraction (RH- T -XRD) method was used to study phase transitions of ferric sulfate hydrates at temperatures from 25 to 80 °C. A dehydration of paracoquimbite to ferric sulfate pentahydrate [Fe 2 (SO 4 ) 3 ·5H 2 O] was identified at 80 °C. The results are discussed with a previously constructed ferric sulfate RH– T phase diagram by Ackermann et al. (2009).

By varying the solvents and temperatures under solvothermal conditions, two new magnesium based coordination networks were synthesized using 2,5-thiophenedicarbxoylate as a linker. Mg3(TDC)3(DMF)3 [1; TDC = 2,5 thiophenedicarboxylate; space group P21/c, a = 17.747(4) A, b = 9.805(2) A, c = 21.359(4) A, β = 103.13(3)°] is constructed by a combination of magnesium polyhedral trimers, which are connected by the TDC2− linkers to form a 3-D network. Coordinated DMF molecules are present within the channels. Mg(TDC)(H2O)2 [2; space group Pnma, a = 7.296(4) A, b = 17.760(4) A, c = 6.6631(3) A] is formed by 1-D chains of magnesium octahedra connected by the TDC2− linker. Water molecules are coordinated at the axial positions of the magnesium octahedra. Compound 1 is formed using DMF as the synthesis solvent at 180 °C, while compound 2 is formed using ethanol as the synthesis solvent at 100 °C. Both compounds show enhanced photoluminescence intensity when excited at 397 nm compared to the free TDC ligand, suggesting a charge transfer between the ligand and the magnesium metal center.

SrRuO3 (SRO) has been studied extensively at the bulk and thin film scales for a variety of applications, such as multilayer devices, field-effect devices, multiferroics, and even ferroelectric random access memory (FeRAM). Conversely, the exploration of SRO nanoscale and submicrometer scale structures in terms of both synthesis and applications has been significantly limited. Herein, we are the first to report on the synthesis of SRO submicrometer-sized particles via a molten-salt method. We have accomplished this by systematically probing experimental parameters such as precursors, type of salt, annealing time, annealing temperature, surfactant, cooling rate, and reaction atmosphere in an effort to predictably control the resulting size, shape, and morphology of the SRO product particles. In particular, by quenching the reaction at a cooling rate of 100 °C/min, we can produce rounded SRO particles averaging 149 ± 100 nm in size. Moreover, with the addition of a mixture of mineral oil in Triton X-100, th...

A three-dimensional magnesium–lithium coordination network, Mg2Li(BTC) (HBTC)(DMF)2, (1) (BTC = 1,3,5-benzenetricarboxylate; DMF = N,N-dimethylformamide), the first example of a mixed-metal Mg–Li coordination network, is synthesized using solvothermal techniques. Structural characterization was completed using single crystal x-ray techniques while thermal properties and surface area measurements were conducted by thermogravimetric and BET analysis, respectively.

Five novel two-dimensional frameworks containing formate-bridged metal-centered octahedra are synthesized ionothermally from two ionic liquids previously unused as solvents in hybrid synthesis, 2-hydroxyethylammonium (HEA) formate, and 1-hydroxy-3-proplyammonium (HPA) formate. Templating effects of the cation from each ionic liquid drive the formation of different structures. [NH(3)C(2)H(4)OH](2)[M(CHO(2))(4)] (1: M = Co, 2: M = Ni) exhibit the same stoichiometry and connectivity as their manganese analogue (3: M = Mn), but the manganese form exhibits a different topology from 1 and 2. [NH(3)C(3)H(6)OH][M(CHO(2))(3)(H(2)O)] (4: M = Co, 5: M = Mn) were synthesized using the HPA formate ionic liquid with a metal-formate connectivity related to those of 1-3. Canted antiferromagnetic ordering occurs at low temperatures (1: T(N) = 7.0 K, 2: T(N) = 4.6 K, 3: T(N) = 8.0 K, 4: T(N) = 7.0 K, 5: T(N) = 9.2 K), similar to the magnetic properties previously reported for other metal-formate hybrid materials.

A gallium-based metal-organic framework Ga(6)(C(9)H(3)O(6))(8)·(C(2)H(8)N)(6)(C(3)H(7)NO)(3)(H(2)O)(26) [1, Ga(6)(1,3,5-BTC)(8)·6DMA·3DMF·26H(2)O], GaMOF-1; BTC = benzenetricarboxylate/trimesic acid and DMA = dimethylamine], with space group I43d, a = 19.611(1) Å, and V = 7953.4(6) Å(3), was synthesized using solvothermal techniques and characterized by synchrotron-based X-ray microcrystal diffraction. Compound 1 contains isolated gallium tetrahedra connected by the organic linker (BTC) forming a 3,4-connected anionic porous network. Disordered positively charged ions and solvent molecules are present in the pore, compensating for the negative charge of the framework. These positively charged molecules could be exchanged with alkali-metal ions, as is evident by an ICP-MS study. The H(2) storage capacity of the parent framework is moderate with a H(2) storage capacity of ~0.5 wt % at 77 K and 1 atm.

Background In nature or in the laboratory, the roughly spherical interior of the ferritin protein is well suited for the formation and storage of a variety of nanosized metal oxy-hydroxide compounds which hold promise for a range of applications. However, the linkages between ferritin reactivity and the structure and physicochemical properties of the nanoparticle core, either native or reconstituted, remain only partly understood. Scope of review Here we review studies, including those from our laboratory, which have investigated the structure of ferritin-derived ferrihydrite and reactivity of ferritin, both native and reconstituted. Selected proposed structure models for ferrihydrite are discussed along with the structural and genetic relationships that exist among several different forms of ferrihydrite. With regard to reactivity, the review will emphasize studies that have investigated the (photo)reactivity of ferritin and ferritin-derived materials with environmentally relevant gaseous and aqueous species. Major conclusions The inorganic core formed from apoferritin reconstituted with varied amounts of Fe has the same structural topology as the inorganically derived ferrihydrite that is an important component of many environmental and soil systems. Reactivity of ferritin toward aqueous species resulting from the photoexcitation of the inorganic core of the protein shows promise for driving redox reactions relevant to environmental chemistry. General significance Ferritin-derived ferrihydrite is effectively maintained in a relatively unaggregated state, which improves reactivity and opens the possibility of future applications in environmental remediation. Advances in our understanding of the structure, composition, and disorder in synthetic, inorganically derived ferrihydrite are shedding new light on the reactivity and stability of ferrihydrite derived artificially from ferritin.

Chromium(III) (oxy)hydroxide and mixed Cr(III)−Fe(III) (oxy)hydroxides are environmentally important compounds for controlling chromium speciation and bioaccessibility in soils and aquatic systems and are also industrially important as precursors for materials and catalyst synthesis. However, direct characterization of the atomic arrangements of these materials is complicated because of their amorphous X-ray properties. This study involves synthesis of the complete Cr(III)−Fe(III) (oxy)hydroxide compositional series, and the use of complementary thermal, microscopic, spectroscopic, and scattering techniques for the evaluation of their structural properties. Thermal analysis results show that the Cr end member has a higher hydration state than the Fe end member, likely associated with the difference in water exchange rates in the first hydration spheres of Cr(III) and Fe(III). Three stages of weight loss are observed and are likely related to the loss of surface/structural water and hydroxyl groups. As com...

A 3-D lithium based metal organic framework Li2(C7H3NO4)·(C3H7NO) [Li2(2,5-PDC)·(DMF), 1; ULMOF-5, UL= ultralight, PDC = pyridinedicarboxylate, space group Pbcn, a = 15.800(3) A, b = 8.5958(17) A, c = 18.460(4) A, V = 2507.1(9) A3] was synthesized using the solvothermal method and characterized by single crystal and powder X-ray diffraction techniques. Compound 1 contains tetrameric edge and corner sharing lithium polyhedral clusters connected by organic linkers, forming channels along the [001] direction, with coordinated DMF molecules pointing toward each other in these channels. Thermogravimetric analysis shows compound 1 is stable up to 280 °C under N2 atmosphere followed by removal of the coordinated DMF molecules, as evident from the associated weight loss. BET (25.06 m2/g) surface area measurement showed loss of porosity after solvent removal because of a structure change. Solid-state 6Li NMR on the desolvated compound showed the absence of tricoordinated lithium centers, indicating rearrangement o...

We employed ab initio evolutionary algorithm USPEX to speed up the discovery of a novel oxynitride in the binary system of GaN-TiO2 using high-pressure synthesis. A 1:2 mixture of GaN and nanocrystalline TiO2 (anatase) was reacted under 1 GPa of pressure and at 1200 °C in a piston cylinder apparatus to produce a mixture of TiO2 (rutile) and an unknown phase. From the initial analysis of high resolution neutron and X-ray diffraction data, it is isomorphic with monoclinic V2GaO5 with a unit cell composition of Ga10Ti8O28N2 with the following parameters: monoclinic, space group C2/m, a = 17.823(1) Å, b = 2.9970(1) Å, c = 9.4205(5) Å, β = 98.446(3)°; Volume = 497.74(3) Å3. Further, a joint rietveld refinement revealed two distinct regimes—A Ti-rich block and a Ga-rich block. The Ti-rich block consists of four edge-shared octahedra and contains a site which is about 60% occupied by N; this site is bonded to four Ti. The remainder of the block consists of edge linked Ti-octahedral chains linked to the TiN/TiO fragments at octahedral corners partially occupied by nitrogen. The Ga-block contains two symmetry independent octahedral sites, occupied mostly by Ga, and a pure Ga-centered tetrahedral site bonded mostly to oxygen.

Differential pair distribution function (d-PDF) analysis of high energy powder X-ray diffraction data was carried out on 2-line ferrihydrite nanoparticles with arsenate oxyanions adsorbed on the surface to investigate the binding mechanism. In this analysis, a PDF of ferrihydrite is subtracted from a PDF of ferrihydrite with arsenate sorbed on the surface, leaving only correlations from within the surface layer and between the surface and the particle. As-O and As-Fe correlations were observed at 1.68 and 3.29 A, respectively, in good agreement with previously published EXAFS data, confirming a bidentate binuclear binding mechanism. Further peaks are observed in the d-PDF which are not present in EXAFS, corresponding to correlations between As and O in the particle and As-2nd Fe.

Phases encountered in the hydration of monoclinic and trigonal anhydrous Fe2(SO4)3 and evaporation of Fe2(SO4)3 solutions at room temperature were determined using in situ and ex situ X-ray diffraction (XRD) under dynamic relative humidity (RH) control at room temperature (22–25 °C). Both monoclinic and trigonal forms of Fe2(SO4)3 remain anhydrous at 11% RH or below, and undergo the following phase evolution sequence: anhydrous Fe2(SO4)3 → (ferricopiapite, rhomboclase) → kornelite → paracoquimbite at RH between 33 and 53% as a function of time. Evaporation of aqueous Fe2(SO4)3 solutions at 40% < RH < 60% results in precipitation of ferricopiapite and rhomboclase during evaporation, followed by a transition to kornelite and then paracoquimbite. Evaporation at RH < 33% produced an amorphous ferric-sulfate phase. The presence of some iron sulfate hydrates and their stability under varying RH are not only determined by the final humidity level, but also the intermediate stages and hydration history (i.e., either ferricopiapite or paracoquimbite can be a stable phase at 62% RH depending on the hydration history). The sensitivity to humidity change and path-dependent transitions of ferric sulfates make them potentially valuable indicators of paleo-environmental conditions and past water activity on Mars. The phase relationships reported herein can help in understanding the diagenesis of ferric sulfate minerals, and are applicable to geochemical modeling of mineral solubility in multi-component systems, an endeavor hindered by the need for fundamental laboratory studies of iron sulfate hydrates.

Inspired by close-packing of spheres, to strengthen the framework-H{sub 2} interaction in MOFs (metal-organic frameworks), a strategy is devised to increase the number of nearest neighboring open metal sites ofe ach H{sub 2}-hosting cage, and to align the open metal sites toward the H{sub 2} molecules. Two MOF polymorphs were made, one exhibiting a record high hydrogen uptake of 3.0 wt% at 1 bar and 77 k.

The mixed addenda isopolyanion, [N(CH 3 ) 4 ] 2 Na 2 [cis-Nb 2 W 4 O 19 ]·18H 2 O, reacts with Cu(NO 3 ) 2 in water and in the presence of NH 2 CH 2 CH 2 NH 2 (en) or NH 4 OH at 60 °C to yield a phase that is decorated {[Cu(en) 2 (H 2 O)] 2 -[Nb 2 W 4 O 19 ]·2H 2 O (1)) or charge-balanced {[Cu(NH 3 ) 4 -(H20)] 2 [Nb 2 W 4 O 19 ]·8H 2 O (2)), respectively, by (amine)copper complexes. The prolonged heating at 95 °C of [N(CH 3 ) 4 ] 6 -[Nb 10 O 28 ]·6H 2 O, [N(CH3)4] 2 Na 2 [cis-Nb 2 W 4 O 19 ]·18H 2 O, or Na4K2[cis-Nb 4 W 2 O 19 ]·12H 2 O and Cu(NO 3 ) 2 in a mixed water/amine [en or NH 2 CH 2 CH 2 CH 2 NH 2 (dap)] solution results in the formation of two-dimensional materials with alternate layers of (amine)copper complexes linking Lindqvist [Nb 6-x W x O 19 ] (8-x)- (x = 0-4) clusters. These phases include: [Cu(dap) 2 ] 3 [Nb 4 W 2 O 19 ]·7H 2 O (3), [Cu(dap) 2 ] 3 -[H 2 Nb 6 O 19 ]·6H 2 O (4), [Cu(dap) 2 ] 3 [Nb 3 W 3 O 19 ]-Cl·6H 2 O (5), and [Cu(en) 2 ] 3 [Nb 4 W 2 O 19 ]·6H 2 O (6). Complexes 4 and 5 result from the decomposition of [Nb 10 O 28 ] 6- and [cis-Nb 2 W 4 O 19 ] 4- to [H 2 Nb 6 O 19 ] 6- and [fac-Nb 3 W 3 O 19 ] 5- , respectively, in alkaline solution. Complex 5 contains an extra-framework site that is occupied by Cl - , but this site is occupied by a water molecule in 3 and is vacant in structures 4 and 6. The results of this study suggest that charge density, cluster charge and symmetry, and cluster-cation pairing are all important parameters in the incorporation of d-electron metals onto the surfaces of [Nb 6-x W x O 19 ] (8-x)- (x = 0-4) clusters or into the frameworks of Lindqvist-based complex materials.

The highly charged dodecaniobate Keggin ions [XNb12O40](-16) (X = Si, Ge) and [XNb12O40](-15) (X = P) serve as building blocks of self-assembled, low-dimensional anionic framework materials. In addition to its high charge, the Keggin ion provides optimal binding geometries that render these materials as attractive metal sorbents and ion exchangers. We describe here the synthesis and single-crystal X-ray structure of K(10-x)[Nb2O2][HxGeNb12O40].11H2O (GeNb12-2d; x = approximately 1-1.5), a phase featuring 2D linkage of [GeNb12O40](-16) Keggin ions interlayered with charge-balancing K(+) cations and water molecules. Thermogravimetry, infrared spectroscopy (IR), 1H MAS NMR, and D2O exchange experiments as well as computational studies were used to describe the location and behavior of these interlayer, extraframework species. To model the basicity of the different types of framework oxygen sites appropriately, atomic-centered partial charges were derived from density functional theory (DFT) calculations to model the electrostatic potential. This model enabled the locations and bonding of K(+) cations associated with the framework, as well as K(+) cations bound predominantly to water in the interlayer space, to be accurately computed via Monte Carlo simulation. The poorest agreement between experimental and simulation results was observed for potassium sites that were associated with disordered portions of the framework, namely, the [Nb2O2](6+) bridge between Keggin ions. Finally, through grand canonical Monte Carlo (GCMC) calculations, saturation water loadings consistent with experimental measurements were computed.

A porous hybrid inorganic/organic material, NaNi3(OH)(SIP)2 [SIP = 5-sulfoisophthalate] [1], is shown to strongly bind molecular hydrogen at coordinatively unsaturated metal sites. A combination of H2 sorption isotherms, temperature programmed desorption, and inelastic neutron scattering spectroscopy show the existence of a considerable number of such strong binding sites in [1] along with other sites where hydrogen is more weakly physisorbed. The overall capacity for hydrogen of this material as well as the much stronger binding of hydrogen than in typical porous material represent an important step toward a possible utilization of porous media for hydrogen storage.

Recent studies exploring the role of metal sulfides as (photo)catalysts in prebiotic synthesis reactions provide the impetus for finding carbon-free synthesis methods for metal sulfides. The decomposition of organosulfur and organometallic precursor compounds is often the protocol for synthesizing bulk metal chalcogenides, such as manganese sulfide (MnS). Here we report a hydrothermal synthesis method for the formation of MnS in which a MnCl2 solution is injected into a preheated sulfide solution. By varying the temperature of injection and subsequent aging time, we can control the specific crystal phase of the product. Three MnS polymorphs are known, and two of these, α-MnS and γ-MnS, form as pure phases in aqueous systems. The initial precipitate formed upon mixing of aqueous solutions of Mn2+ and S2- at ambient temperature is nanocrystalline and is composed of a mixture of γ-MnS (wurtzite structure) and β-MnS (zinc blende structure). β-MnS has not previously been identified as forming under aqueous con...

Pressure responses of hydrogen bonding interactions were compared between potassium hydrogen carbonate (KHCO3) and sodium hydrogen carbonate (NaHCO3). KHCO3 undergoes a pressure-induced structural change at 2.8 GPa and room temperature whereas no phase transition has been found so far for NaHCO3 up to 11 GPa. KHCO3 exhibits a substantial decrease in the O-H O angle with increasing pressure. This change could be a trigger for the phase transition at 2.8 GPa. By contrast, no significant change in O-H O angle was observed for NaHCO3 up to 7 GPa. Based on the observations using neutron diffraction, X-ray diffraction and vibrational spectroscopy at high pressure, a possible mechanism for the phase transition of KHCO3 is suggested. In addition, the phase boundary of KHCO3 caused by the pressure-induced transition was determined using in situ Raman spectroscopy at high pressure.

Titanium silicate (TS) with sitinakite topology and composition Na2Ti2O3SiO4·2H2O has received considerable attention because of its high ion-exchange selectivity toward cesium and strontium. In this paper we report the results of the studies of the crystallization process of TS with a combination of ex and in situ experiments. The effects of various parameters, such as gel composition, time, and temperature of the synthesis, on crystallinity and composition of the final product have been investigated. In situ X-ray powder diffraction studies carried out during the synthesis of TS revealed that the process begins with the formation of layered sodium nonatitanate (SNT) with chemical composition Na4Ti9O20·xH2O, which is also an excellent ion exchanger, selective for strontium and actinides. The pathway of transformation of SNT to the final product is sensitive to alkalinity of the starting gels. At high hydroxide concentration the reaction resulted in the formation of sodium titanium oxide silicate, Na2TiSi...

A new polymorph of NaSbO(3) has been synthesized at 10.5 GPa and 1150 degrees C in a uniaxial split sphere anvil type press (USSA-2000) and recovered back to ambient conditions. The high-pressure form of NaSbO(3) adopts an orthorhombically distorted perovskite structure, isostructural with CaTiO(3), GdFeO(3), and NaTaO(3). The space group is Pnma, and the unit cell dimensions are a = 5.43835(6) A, b = 7.66195(8) A, c = 5.38201(5) A. It is a white insulator with an optical band gap of 3.4 eV. This compound represents the first ternary perovskite prepared containing Sb(5+) on the octahedral site. The octahedral tilting distortion in this compound is much larger than expected from ionic radii considerations. The distortion is driven by a second-order Jahn-Teller distortion originating on oxygen that can be traced back to strong Sb-O covalent bonding. A conflict arises between the strong covalent bonding interactions at oxygen that favor a large octahedral tilting distortion and the repulsive Na-O interactions that oppose excessive octahedral tilting. This conflict destabilizes the perovskite topology, thereby stabilizing the ilmenite polymorph under ambient conditions. Analysis of ionic and covalent bonding explains why ASbO(3) and ABiO(3) compositions frequently adopt structures that violate Pauling's rules.

The recent expansion of zeolitic synthesis toward mixed geometry frameworks reflects their potential applications in shape-selective catalysis and absorption. Four scandium phosphates with three-dimensional frameworks have been hydrothermally synthesized. All structures were solved from single-crystal X-ray diffraction and were supported by 31P MAS NMR and infrared spectroscopy. Structure 1 ((C2N2H10)8Sc8(ScO2)4(PO4)4(HPO4)12·12H2O) consists of a novel framework with 14-membered rings (MRs) and 10-MR channels along the a and c axes, respectively. Ethylenediamine and water reside in the resulting supercage. Structure 2 ((C2N2H10)2Sc4(HPO4)8) consists of a framework built from the corner-sharing of ScO6 octahedra with HPO4 tetrahedra whose connection results in a 8-MR channel down the a axis, where hydrolyzed cyclam resides. This compound is isostructural to a number of existing synthetic materials including a scandium phosphate, an indium phosphate, and an iron phosphate. Structure 3 (Sc4(HPO4)8·4(H3O)) is...

The influence of synthesis conditions on the formation of yttrium aluminum garnet (YAG) powders starting from the same solution precursors was investigated by employing a citrate–nitrate gel combustion process and a precursor plasma spraying technique. YAG powders were formed at ≥500 °C, through the citrate–nitrate gel combustion process, without any intermediate phase formation. Time-resolved x-ray experiments were performed for the first time on these citrate–nitrate precursor materials to understand their mode of decomposition. The in situ data confirmed a single-step conversion to YAG from the precursor powder without any intermediate phase formation. Ex situ experiments also produced similar results. However, the use of the same citrate–nitrate precursor solution as a liquid feedstock material in the precursor plasma spraying technique revealed an entirely different transformation mechanism to YAG through intermediate phases like H–YalO3 and O–YalO3.

Synchrotron X-ray single-crystal diffraction analyses revealed that as-synthesized and Na-exchanged RUB-29 (Cs 1− x , Na x ) 14 Li 24 [Si 72 Li 18 O 172 ]· y H 2 O ( x =0, 0.9) displays the lattice symmetry I 222. With increasing ion-exchange time, the Na cations preferentially replace Cs in the larger sites located at the intersections of the 10MR/10MR/8MR channels. The smaller Cs sites are then replaced. While Na cations are easily incorporated on the Cs sites, most of non-framework Li cations remain in the channel system. Relocation of Li cations onto new sites within the channels was observed only after 13 days of ion exchange. Using high-field (14.1 T) NMR spectroscopy, at least six separate 6 Li resonances could be resolved for the first time by solid-state 6 Li MAS NMR spectroscopy and assigned to Li in the framework and non-framework sites of the microporous lithosilicate materials. The fate of Li in both framework and extra-framework sites during exchange was also followed by 6 Li MAS NMR spectroscopy with an Na-exchanged RUB-29 powder sample.

The crystal structures of the compounds BaMGaO4 (M = Al, Fe) have been investigated using conventional single-crystal X-ray diffraction data for M = Fe and with synchrotron radiation data for M = Al. BaAlGaO4 (space group P6322, a = 5.2788(4) Å and c = 8.7835(7) Å, V = 211.97(4) Å3, Z = 2, D calc. = 4.67 g cm–3, wR2 = 0.089 for 242 independent reflections with I > 2σ(I)) is isostructural with BaAl2O4-I. Main building units are layers of six-membered rings of (Al,Ga)O4-tetrahedra perpendicular to [001]. The sequence of directedness of the tetrahedral apices in all single six membered rings (S6R) is UDUDUD (U: up, D: down). Stacking of layers parallel to c results in a three-dimensional framework containing tunnels, where the Ba atoms are located. They are coordinated by nine oxygen ligands in form of distorted tricapped trigonal antiprisms. BaFeGaO4 also belongs to the hexagonal crystal system (space group P63, a = 10.8377(6) Å and c = 8.6865(6) Å, V = 883.59(9) Å3, Z = 8, D calc. = 4.92 g cm–3, wR2 = 0.099 for 1042 independent observed reflections). The crystal showed twinning by merohedry which was accounted for in the refinement calculations. Within a single tetrahedral layer of the framework structure two different types of ditrigonal-shaped rings are distinguishable: one fourth of the rings have an UDUDUD topology, whereas the sequence of the remaining rings is UUUDDD. The Fe3+- and Ga3+-cations show an ordered distribution among the four symmetrically independent T-sites: two positions contain either Fe or Ga, whereas on the remaining two sites there is a definite preference for one of the two cation species. The Ba atoms in the cavities of the framework are coordinated by eight to nine oxygen neighbors. The observed twinning in BaFeGaO4 can be attributed to the existence of pseudo twofold axis within the tetrahedral layers, running parallel [100] and the corresponding symmetrically equivalent directions.

Sandia octahedral molecular sieves (SOMS) is an isostructural, variable composition class of ion exchangers with the general formula Na(2)Nb(2-x)M(IV)(x)O (6-x)(OH)(x).H(2)O (M(IV) = Ti, Zr; x = 0.04-0.40) where up to 20% of the framework Nb(V) can be substituted with Ti(IV) or Zr(IV). This class of molecular sieves is easily converted to perovskite through low-temperature heat treatment (500-600 degrees C). This report provides a detailed account of how the charge imbalance of this Nb(V)-M(IV) substitution is compensated. X-ray powder diffraction with Rietveld refinement, infrared spectroscopy, thermogravimetric analysis, (23)Na MAS NMR, and (1)H MAS NMR were used to determine how the framework anionic charge is cation-balanced over a range of framework compositions. All spectroscopic evidence indicated a proton addition for each M(IV) substitution. Evidences for variable proton content included (1) increasing OH observed by (1)H MAS NMR with increasing M(IV) substitution, (2) increased infrared band broadening indicating increased H-bonding with increasing M(IV) substitution, (3) increased TGA weight loss (due to increased OH content) with increasing M(IV) substitution, (4) no variance in population on the sodium sites (indicated by Rietveld refinement) with variable composition, and (5) no change in the (23)Na MAS NMR spectra with variable composition. Also observed by infrared spectroscopy and (23)Na MAS NMR was increased disorder on the Nb(V)/M(IV) framework sites with increasing M(IV) substitution, evidenced by broadening of these spectral features. These spectroscopic studies, along with ion exchange experiments, also revealed the effect of the Nb(V)/M(IV) framework substitution on materials properties. Namely, the temperature of conversion to NaNb(1-x)M(IV)(x)O(3) (M = Ti, Zr) perovskite increased with increasing Ti in the framework and decreased with increasing Zr in the framework. This suggested that Ti stabilizes the SOMS framework and Zr destabilizes the SOMS framework. Finally, comparing ion exchange properties of a SOMS material with minimal (2%) Ti to a SOMS material with maximum (20%) Ti revealed the divalent cation selectivity of these materials which was reported previously is a function of the M(IV) substitution in the framework. A thorough investigation of this class of SOMS materials has revealed the importance of understanding the influence of heterovalent substitutions in microporous frameworks on material properties.