Phosphate Tetrahedra Research Articles

Spectroscopic studies on natural fluorapatites irradiated with 10 MeV electrons

Fluorapatites are one of the candidate matrices for hosting the nuclear waste from molten salt reactors. To assess their radiation stability and long-term performance, natural analogue study approach was undertaken. Naturally occurring fluorapatites containing with carbonate substitutions were irradiated with 10 MeV electron beam radiation for doses 20 MGy. X-ray diffraction, Raman and Fourier Transform infrared spectroscopy show no evidence of structural degradation or phosphate condensation. However, a change in the intensity of ν3 Phosphate Raman bands was observed indicating that the phosphate tetrahedra is affected by the electron beam consistent with the displacement cross-section calculations for each constituent element. Overall, the study confirmed that fluorapatite possess good structural stability against electron radiation upto 20 MGy.

FT-Raman spectroscopic and electrical investigations of RE3+ doped multi-functional silicate glasses for cathode plating and integrated microelectronic technology

Lanthanide-doped silicate glasses were subjected to structural and temperature-dependent electrical investigations to validate their multi-functionality in the integrated microelectronic industries. Raman-active vibrations around 920 cm−1 and 1330 cm−1 confirmed the silicate and phosphate tetrahedra respectively. The Er3+ doped glass demonstrated the highest dielectric constant of 9.21 × 105, while Sm3+ infused glass exhibited the lowest dielectric constant of 4.37 × 104 at 0.1 Hz and 473 K. The Sm3+ doped glasses are prospective for plating on copper chips in printed circuit boards that necessitate low dielectric constants to minimize propagation delay. The equivalent circuitry fitted for the Nyquist impedance plot of Er3+ doped glass constituted parallel combinations of a resistor and Constant Phase Element (CPE), in series with Warburg diffusion impedance. The CPE approaching a capacitive nature in the Er3+ doped glass could be suggested for cathode plating in batteries, and fabrication of multi-layer dielectric substrates in radio frequency condensers.

Structural and spectroscopic insights into the performance of K3Tb(PO4)2 green phosphor.

A narrow-band green emitting K3Tb(PO4)2 phosphor has been synthesized by a novel single-crystal growth approach involving the application of an inert flux. Its structural and spectroscopic peculiarities have been systematically studied by means of single-crystal X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy analysis, and diffuse reflectance, infrared and photoluminescence spectroscopy. The layered framework of the title compound is organized by linking together slightly distorted phosphate tetrahedra with non-condensed TbO7 polyhedra into [Tb(PO4)2]3- sheets interconnected by potassium cations. K3Tb(PO4)2 reveals an intense slow green photoluminescence (PL) (decay time constant τ is near 2.6 ms) under excitation in the range from VUV (100 nm) up to blue light (484 nm). Intensive narrow lines of the 5D4 → 7F6-0 (4f8 → 4f8) radiative transitions in Tb3+ ions form the PL spectra. Besides, fast violet PL (time constant τ < 20 ns) occurs under PL excitations in a narrow range from 250 to 325 nm. Dependencies of the PL quantum yield, and the green and violet PL decays on the excitation wavelength have been analyzed taking into account the multi-phonons, cross-relaxation processes and exciting light absorption by the inherent defects in the K3Tb(PO4)2 crystal lattice. The dependency of the complex characteristics of PL quantum yield on the excitation wavelength and violet photoluminescence is ascribed to the formation of Tb4+ ions. The color coordinates and color purity of the emission were estimated for the cases of PL excitation in the 160-371 nm spectral range. It has been shown that these characteristics are similar to or even better than those reported for conventional commercial green phosphors. The high values of correlated color temperature (T> 4863 K) of the emission indicates the potential use of K3Tb(PO4)2 for enhancing cold-light emitting devices.

Influence of pairs of alkali metal cations on the formation of complex phosphates at the crystallization of multicomponent self-fluxes

The regularities of phase formation in the systems (МІ1 + МІ2)2O—P2O5—TiO2—МІІO (МІ — Na, K, Rb; MII — Mg, Co, Ni) at the crystallization of multicomponent self-fluxes at the values of molar ratios: (МІ1 + МІ2)/Р = 1.0; Ti/Р = 0.25; MII/Ті = 1.0, and М І 1/М І 2 = 1.0 and 2.0 over the temperature interval of 1000-780 °C have been investigated. For mixed sodium-potassium-phosphate systems, regardless of the ratio of Na/K (1.0 or 2.0), the solidification without crystal formation was found. For Na/Rb-containing systems, the increasing of the so dium amount in the initial melt to the value of molar ratio Na/Rb = 2.0 promoted the crystalization of single crystals of NaTi2(PO4)3 doped by divalent metals ions. In the case of K-Rb-phosphate self-fluxes, it was found that the value of K/Rb = 2.0 is optimal for the growing of langbeinite-related single crystals (K/Rb)2MII0,5Ti1,5(PO4)3 (MII — Mg, Co, Ni) which belong to cubic system (space group P213). The calculated cell parameters for new phosphates (K/Rb)2MII 0.5Ti1.5(PO4)3 depend on the nature of MII: a = 9.851(6) Å for Mg, a = 9.853(9) Å for Co and a = 9.850 (1) - for Ni. In the FTIR spectra of phosphates (K/Rb)2MII0.5Ti1.5(PO4)3, the characteristic modes in the region of 520-650 сm–1 and 1000-1250 сm-1 which have been assigned to symmetric and asymmetric stretching vibrations (ν4, ν1 and ν3) of phosphate tetrahedron confirmed the presence of orthophosphate type anion in their composition. According to results of thermal analysis, the melting points of (K/Rb)2MII0.5Ti1.5(PO4)3 are at a temperatures of 1082 °С for MII — Ni, 1057 °С for MII — Co, and above 1100 °С for MII — Mg. The synthesized complex phosphates have been investigated using the powder X-Ray diffraction method, thermogravimetry, differential thermal analysis, and FTIR-spectroscopy.

TlPO3 and its comparison with isotypic RbPO3 and CsPO3.

The crystal structure of thallium(I) catena-polyphosphate, TlPO3, contains a polyphosphate chain extending parallel to [010] with a repeating unit of two phosphate tetra-hedra. The TlI atom is located in-between the polyphosphate chains and is bonded by oxygen atoms in a distorted [6+1] coordination in the form of a monocapped prism, with the longest Tl-O bond to the bridging O atom of the polyphosphate chain. A qu-anti-tative structural comparison with isotypic RbPO3 and CsPO3 reveals that the usually pronounced stereoactivity of the 6s 2 lone pair at the TlI atom is not apparent in the case of TlPO3.

Thermochemical studies of X(NpO2)(PO4)(H2O)3 (X = K+, Rb+), neptunium analogs of the autunite/meta-autunite group

Actinide phosphate materials with autunite or meta-autunite type sheets consisting of vertex-sharing actinyl square bipyramids and phosphate tetrahedra have low aqueous solubility and potential applications for actinide immobilization in the environment. Neptunyl phosphates, X(NpO2)(PO4)(H2O)3, X ​= ​K+ and Rb+, have been synthesized by hydrothermal reactions and characterized for their structures and purities. Direct thermochemical studies were performed using high temperature oxide melt drop solution calorimetry. After correcting for the presence of residual fluorapatite from the synthesis, the formation enthalpies of K(NpO2)(PO4)(H2O)3 and Rb(NpO2)(PO4)(H2O)3 are determined to be −3235 ​± ​21 ​kJ/mol and −3270 ​± ​11 ​kJ/mol, respectively. The thermodynamic data presented here may be important for understanding neptunium mobility after disposal of nuclear waste in a geological repository.

Structural Role of Phosphate in Metaluminous Sodium Aluminosilicate Glasses As Studied by Solid State NMR Spectroscopy

In this contribution we present a detailed study of the effect of the addition of small to intermediate amounts of P2O5 (up to 7.5 mol %) on the network organization of metaluminous sodium aluminosilicate glasses employing a range of advanced solid state NMR methodologies. The combined results from MAS, MQMAS (multiple quantum MAS), or MAT (magic angle turning) NMR spectroscopy and a variety of dipolar based NMR experiments-27Al{31P}-, 27Al{29Si}-, 29Si{31P}-, and 31P{29Si}-REDOR (rotational echo double resonance) NMR spectroscopy as well as 31P{27Al}- and 29Si{27Al}-REAPDOR (rotational echo adiabatic passage double resonance) NMR-allow for a detailed analysis of the network organization adopted by these glasses. Phosphate is found as QP2, QP3, and QP4 (with the superscript denoting the number of bridging oxygens), the QP4 units can be safely identified with the help of 31P MAT NMR experiments. Al exclusively adopts a 4-fold coordination. The withdrawal of a fraction of the sodium cations from AlO4 units that is needed for charge compensation of the QP2 units necessitates an alternative charge compensation scheme for these AlO4 units via formation of QP4 units or oxygen triclusters. The dipolar NMR experiments suggest a strong preference of P for Al with an average value of ca. 2.4 P-O-Al connections per phosphate tetrahedron. P is thus mainly integrated into the network via P-O-Al bonding, the formation of Si-O-P bonding plays only a minor role.

CИНТЕЗ, ДОСЛІДЖЕННЯ ТА ПРОВІДНІ ВЛАСТИВОСТІ ФАЗ АЛЮОДИТОВОГО ТИПУ

Complex oxide phosphates Na1.5Co1.5Fe1.5(PO4)3, Na1.75Co1.75Fe1.25(PO4)3, Na2Co2Fe(PO4)3 and Li0.25Na1.75Co2Fe(PO4)3, belonging to the alluaudite structural type (monoclinic system, space group C2/c) were synthesized by the melting method with further annealing of the homogenous glasses at a temperature 600°C. According to powder X-ray diffraction data the partial substitution of sodium cations by lithium cations in the initial phosphate matrix Na2Co2Fe(PO4)3 led to decreasing of lattice parameters for Li0.25Na1.75Co2Fe(PO4)3 (a = 11.7572(3) Å, b = 12.4528(4) Å, c = 6.4416(2) Å and β = 113.911(1)°). The FTIR-spectroscopy results confirmed the presence of PO4-tetrahedra in the composition of prepared phases. Modes in the regions of 400–600 cm-1 and 900–1000 cm–1 were assigned to symmetric and asymmetric stretching vibrations of phosphate tetrahedron in the alluaudite-type structure, respectively. The effect of partial substitution of sodium cations by lithium cations in the phosphate matrix Na2Co2Fe(PO4)3 as well as the decrease of sodium cations amounts in the alluauditerelated structure for the phases of Na1.5Co1.5Fe1.5(PO4)3 and Na1.75Co1.75Fe1.25(PO4)3 on the conductive properties of compounds were analyzed. It was found that increasing of sodium cations amount in the channels of the alluaudite-related structure leads to an increase of the specific conductivity from 0.011 Om-1m-1 for Na1.75Co1.75Fe1.25(PO4)3 to 0.15 Om–1m–1 for Na2Co2Fe(PO4)3 at a temperature of 550 °C. It was also found that partial substitution of sodium cations by lithium cations in the initial phosphate matrix Na2Co2Fe(PO4)3 no significant influence on conductivity of phase Li0.25Na1.75Co2Fe(PO4)3 (σ = 0.095 Оm–1m–1 at a temperature of 550 °C). In the case of phosphates Na1.75Co1.75Fe1.25(PO4)3 and Li0.25Na1.75Co2Fe(PO4)3 decreasing of conductive properties in the temperature ranges 190–250 °С and 550–590 °С, respectively are caused by contribution of different components in general conductivity. The synthesized phases can be used in the development of materials with conductive properties.

Geochemistry of Phosphorite and Associated Rocks of Akashat Formation (Middle Paleocene) in Akashat Mine, Iraqi Western Desert. Part II: Trace Elements

Akashat Formation is an important formation due to its content of the Hirri member, which includes phosphorites and phosphatic limestones, that are rich in P2O5. These rocks are mainly composed of apatite and calcite. In addition to other minor and trace minerals like palygorskite, quartz, dolomite and secondary gypsum. All these minerals are hosted the most trace elements in the Akashat rocks. U, Sr, Y and Zr are related to apatite more than other minerals. While Ga, Rb and Ti are almost correlated with the clay minerals. The rest trace elements are distributed among other minerals and organic matter. The hosting of trace elements by a mineral takes place in many cases as substituted in Ca(I), Ca(II) and phosphate tetrahedron in Francolite, Ca site in calcite, in clay mineral phases, or adsorbed on clay mineral faces, organic matters and in the crystal channel of francolite.

Sic Parvis Magna: Manganese-Substituted Tricalcium Phosphate and Its Biophysical Properties.

Succeeding in the substitution of pharmaceutical compounds with ions deliverable with the use of resorbable biomaterials could have far-reaching benefits for medicine and economy. Calcium phosphates are known as excellent accommodators of foreign ions. Manganese, the fifth most abundant metal on Earth was studied here as an ionic dopant in β-tricalcium phosphate (β-TCP) ceramics. β-TCP containing different amounts of Mn2+ ions per MnxCa3-x(PO4)2 formula (x = 0, 0.001, 0.01, and 0.1) was investigated for a range of physicochemical and biological properties. The results suggested the role of Mn2+ as a structure booster, not breaker. Mn2+ ions increased the size of coherent X-ray scattering regions averaged across all crystallographic directions and also lowered the temperature of transformation of the hydroxyapatite precursor to β-TCP. The particle size increased fivefold, from 20 to 100 nm, in the 650-750 °C region, indicating that the reaction of formation of β-TCP was accompanied by a considerable degree of grain growth. The splitting of the antisymmetric stretching mode of the phosphate tetrahedron occurred proportionally to the Mn2+ content in the material, while electron paramagnetic resonance spectra suggested that Mn2+ might substitute for three out of five possible calcium ion positions in the unit cell of β-TCP. The biological effects of Mn-free β-TCP and Mn-doped β-TCP were selective: moderately proliferative to mammalian cells, moderately inhibitory to bacteria, and insignificant to fungi. Unlike pure β-TCP, β-TCP doped with the highest concentration of Mn2+ ions significantly inhibited the growth of all bacterial species tested: Staphylococcus aureus, Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa, and Enterococcus faecalis. The overall effect against the Gram-positive bacteria was more intense than against the Gram-negative microorganisms. Meanwhile, β-TCP alone had an augmentative effect of the viability of adipose-derived mesenchymal stem cells (ADMSCs) and the addition of Mn2+ tended to reduce the extent of this augmentative effect, but without imparting any toxicity. For all Mn-doped β-TCP concentrations except the highest, the cell viability after 72 h incubation was significantly higher than that of the negative control. Assays evaluating the effect of Mn2+-containing β-TCP formulations on the differentiation of ADMSCs into three different lineages-osteogenic, adipogenic, and chondrogenic-demonstrated no inhibitory or adverse effects compared to pure β-TCP and powder-free positive controls. Still, β-TCP delivering the lowest amount of Mn2+ seemed most effective in sustaining the differentiation process toward all three phenotypes, indicating that the dose of Mn2+ in β-TCP need not be excessive to be effective.

Aggregating ability of ferric chloride in the presence of phosphate ligand

Complexing anions such as phosphate or silicate play an ambivalent role in the performance of hydrolyzing metal coagulants: On one hand, they significantly interfere with the hydrolytic pathway of conventional iron or aluminum coagulants, the associated destabilization mechanism remaining rather elusive; on the other hand, they have been shown to be key ingredients in the formulation of innovative coagulant solutions exhibiting improved removal efficiency, their action mechanism at the molecular scale being presently poorly understood. In this paper, we explore the effect of small additions of phosphate ligand on the chemical coagulation of silica nanoparticles with ferric chloride. Transmission Electron Microscopy-Energy Dispersed X-ray Spectroscopy (TEM-EDXS) combined with Extended X-ray absorption Fine Structure Spectroscopy (EXAFS) at the Fe K-edge are used to provide an insight into the nature of coagulant species, whereas jar-tests, laser diffraction, Small Angle X-ray Scattering (SAXS), and electrophoretic mobility, are used to investigate the aggregation dynamics of silica particles in the presence of phosphate ligand. We show that, in spite of a slight increase in the consumption of iron coagulant, the addition of phosphate significantly improves the formation of silica aggregates provided that the elemental Fe/P ratio remains above 7. Such effects originate from both a large increase in the overall number of coagulant species, the binding of a phosphate ligand terminating the growth of polymeric chains of edge-sharing Fe octahedra, and a change in the nature of the coagulant species that evolves with the Fe/P ratio, small polycations built-up from Fe-oligomers linked by phosphate tetrahedra being eventually formed. Those non-equilibrium nanosize Fe–P coagulant species assemble the silica nanoparticles to form hetero-aggregates whose structure is consistent with a Diffusion-Limited Cluster Aggregation mechanism.

V-P2O5 micro-clustering in P-doped silica studied by a first-principles Raman investigation

Synthetic vitreous silica is currently the preferred material for the production of optical fibres because of the several excellent properties of this glass, e.g. high transmission in the visible and IR domains, high mechanical strength, chemical durability, and ease of doping with various materials. For instance, fiber lasers and amplifiers exploit the light amplification properties provided by rare-earth ions employed as dopants in the core of silica-based optical fibers. The structure and composition of the nearest neighbor shell surrounding rare-earth ions in silica-based optical fibers and amplifiers have been intensively debated in the last decade. To reduce aggregation effects between rare-earth ions, co-dopants such as phosphorus and aluminium are added as structural modifiers; phosphorus-doping, in particular, has proved to be very efficient in dissolving rare-earth ions. In this work, we provide further insights concerning the embedding of P atoms into the silica network, which may be relevant for explaining the ease of formation of a phosphorus pentoxide nearest-neighbor shell around a rare-earth dopant. In particular, by means of first-principles calculations, we discuss alternative models for an irradiation (UV, x–, γ-rays) induced paramagnetic center, i.e. the so called room-temperature phosphorus-oxygen-hole center, and its precursors. We report that the most likely precursor of a room-temperature phosphorus-oxygen-hole center comprises of a micro-cluster of a few (at least two) neighboring phosphate tetrahedra, and correspondingly that the occurrence of isolated [(O-)2P(=O)2]− units is unlikely even at low P-doping concentrations. In fact, this work predicts that the symmetric stretching of P=O bonds in isolated [(O-)2P(=O)2]− units appears as a Raman band at a frequency of ~1110 cm−1, and only by including at least another corner-sharing phosphate tetrahedron, it is shown to shift to higher frequencies (up to ~40 cm−1) due to the shortening of P=O bonds, thereby leading to an improved agreement with the observed Raman band located at ~1145 cm−1.

QUANTUM-MECHANICAL CALCULATIONS OF THE CARBONATE-CONTAINING CALCIUM APATITES ATOMIC AND ELECTRONIC STRUCTURE

Background. The inclusion of the CO32- ion into the structure of apatite leads to significant changes in the chemical and physical characteristics of the mineral. The growth rate of the hydroxyapatite crystal significantly decreases with carbonate ions, and the resistance of the tooth enamel and bones to acids is reduced. At the same time, the concentration of CO32- in bone apatite controls the shape and size of nanocrystals of this mineral, which is an important condition for the preservation of nanoscale effects of these crystals and, accordingly, plays an important role in the processes of bone metabolism.Objective. The aim of the paper is theoretical study of the effect of the inclusion of CO32- ion into the apatite structure on the atomic and the electronic structure of the mineral.Methods. Calculations within the density functional theory (DFT) using the Wien2k package, which based on the full-potential (linearized) augmented plane-wave ((L)APW) + local orbitals (lo) method, using the Perdew–Burke–Ernzerhof generalized gradient approximation for solids (PBEsol-GGA).Results. Atomic coordinates, bond lengths, total and partial densities of the electronic states of apatites Са10(РO4)6(ОН)2, Са10(РO4)6СО3, Са10(РO4)6ОН(СО3)0.5, Са9N(РO4)5(СО3)(ОН)2 are calculated using the density functional theory. The effect of isomorphic substitution of A and B types on the electronic structure of apatite-like compounds has been investigated. Changes in the atomic structure of apatite are analyzed when CO32- ions are included in its structure, both in the anion and the phosphate tetrahedron positions. Comparison of calculated and experimental data was carried out.Conclusions. It was shown that the structure of the occupied part of the valence bands of both types of isomorphically substituted calcium apatites retains a pronounced band character with different lengths of individual sub-bands. Two energy-separated structural regions were revealed – the upper part of the valence band and the lower part of the valence band – subvalent states. The structure of the middle part of the valence band (the region of valence states with energies from ~14 to 19 eV) is poorly expressed. The main contribution to the formation of the main features of the upper part of the valence band of the studied apatites is made by the hybridized s-, p- and partially d-electronic states of calcium and phosphorus ions. The structure of subvalent states is determined by the s states of oxygen, phosphorus and partly metal. The sublattice of oxygen tetrahedra is decisive in the formation of the shape and main features of the total density of electronic states curve of isomorphically substituted calcium apatites. In the case of B-type substitutions, a significant spatial distortion of the carbonate ion occurs.

Comparative chemical composition analysis of femoral condyles bone tissue in health and in deforming arthrosis

A comparative analysis of the chemical composition of the medial and lateral condyles of the femur in norm and with deforming arthrosis of the third degree is presented. It was found that when the bone tissue of the femur is degraded from the surface, a decrease in crystallinity is observed in depth, quantitative and qualitative changes in the organic bone matrix, in particular, a decrease in the proportion of the protein component, a change in the phase inorganic composition, and an increased degree of substitution of calcium in hydroxyapatite for ions of other metals. And the most dramatic changes are observed in bone tissue located near the pathologically deformed areas. It is shown that the data for normal bone tissue of the lateral and medial condyle of one specimen differ, which can be caused by different degrees of stress on the condyles themselves in the process of vital activity of the organism caused by asymmetry and a different shape of their articular surfaces. With deforming arthrosis in the surface layer of bone tissue, the concentration of calcium and a number of other metals increases, while the proportion of the protein component decreases. It was revealed that in the affected bone replacement of phosphate tetrahedra with carbonate ions occurs, as well as substitution of cations of divalent calcium with ions of other metals such as copper and manganese, and especially ferric cations. This breaks the overall structure of the crystal lattice of hydroxyapatite and affects the biomechanical properties of the surface, in particular, the reduction of trophism and the elasticity of the surface. In osteophyte tests, partial replacement of phosphate groups with carbonate groups occurs. Isomorphic structural substitutions caused by deposition of crystalline impurities lead to a change in the ratio of calcium and phosphorus concentrations. Excessive deposition of calcium salts leads to the formation of osteophytes.

The Effect of Phosphatation and Granulation Zeolite in the Adsorption of Cr(VI)

The purpose of this research to study effect of contact time on adsorption of Cr(VI) ion using Granules Alumino Silico Phosphate (GASP) and the effect of Cr (VI) concentration on adsorption capacity at GASP. The GASF synthesis process is carried out in several main stages: 1) activation of zeolite with addition of HCl, 2) zeolite phosphatation with addition of NH 4 H 2 PO 4 ratio Si/P = 1/6 at 235ᴼC for 5 hours, 3) how make GASP with addition of zeolite phosphate (Alumino Silicone Phosphate) and chitosan gel with a syringe pump speed of 50 mL/min. GASP is characterized using XRF, FT-IR and SAA. The contact time effect is tested using 0.1 g of GASF in K 2 CrO 4 100 mg/L with a contact time variation of 0.5; 1.0; 1.5; 2.0 and 2.5 hours. The concentration effect on adsorption capacity is tested out using 0.1 g of GASP in K 2 CrO 4 with concentration variation 25, 50, 75, 100 and 150 mg / L for 2 hours (optimum contact time). The adsorption capacity can be determined using the Langmuir equation. XRF characterization results showed a decrease in SiO 2 levels of 18.10% and Al 2 O 3 by 2.2% after phosphatation process. FTIR characterization results indicate the presence of O-H, N-H and C-H chitosan on absorption bands 1-3. The success of the phosphatation process was evidenced by the shift of wave numbers to the lower regions in the bands 7, 9 and 12 the absorption of tetrahedral silica and alumina shifted to bands 8, 10 and 13 tetrahedral phosphate uptake in accordance with Hooke's law. The result of the research showed that the optimum contact time occurred in the adsorption process for 2 hours. The concentration variation was directly proportional to the increase of the adsorbed Cr (VI) ion mass. The presence of phosphatation and chitosan addition process can increase the value of adsorption capacity by 48,077 mg / g.

Arsenic in hydrothermal apatite: Oxidation state, mechanism of uptake, and comparison between experiments and nature

Element substitution that occurs during fluid–rock interaction permits assessment of fluid composition and interaction conditions in ancient geological systems, and provides a way to fix contaminants from aqueous solutions. We conducted a series of hydrothermal mineral replacement experiments to determine whether a relationship can be established between arsenic (As) distribution in apatite and fluid chemistry. Calcite crystals were reacted with phosphate solutions spiked with As(V), As(III), and mixed As(III)/As(V) species at 250°C and water-saturated pressure. Arsenic-bearing apatite rims formed in several hours, and within 48h the calcite grains were fully replaced. X-ray Absorption Near-edge Spectroscopy (XANES) data show that As retained the trivalent oxidation state in the fully-reacted apatite grown from solutions containing only As(III). Extended X-ray Fine Spectroscopy (EXAFS) data reveal that these As(III) ions are surrounded by about three oxygen atoms at an AsO bond length close to that of an arsenate group (AsO43−), indicating that they occupy tetrahedral phosphate sites. The three-coordinated As(III)–O3 structure, with three oxygen atoms and one lone electron pair around As(III), was confirmed by geometry optimization using ab initio molecular simulations.The micro-XANES imaging data show that apatite formed from solutions spiked with mixed As(III) and As(V) retained only As(V) after completion of the replacement reaction; in contrast, partially reacted samples revealed a complex distribution of As(V)/As(III) ratios, with As(V) concentrated in the center of the grain and As(III) towards the rim. Most natural apatites from the Ernest Henry iron oxide copper gold deposit, Australia, show predominantly As(V), but two grains retained some As(III) in their core. The As-anomalous amphibolite-facies gneiss from Binntal, Switzerland, only revealed As(V), despite the fact that these apatites in both cases formed under conditions where As(III) is expected to be the dominant As form in hydrothermal fluids.These results show that incorporation of As in apatite is a complicated process, and sensitive to the local fluid composition during crystallization, and that some of the complexity in As zoning in partially reacted apatite may be due to local fluctuations of As(V)/As(III) ratios in the fluid and to kinetic effects during the mineral replacement reaction. Our study shows for the first time that As(III) can be incorporated into the apatite structure, although not as efficiently as As(V). Uptake of As(III) is probably highly dependent on the reaction mechanism. As(III)O33− moieties replace phosphate groups, but cause a high strain on the lattice; as a result, As(III) is easily exchanged (or oxidized) for As(V) during hydrothermal recrystallization, and the fully reacted grains only record the preferred oxidation state (i.e., As(V)) from mixed-oxidation state solutions. Overall this study shows that the observed oxidation state of As in apatite may not reflect the original As(III)/As(V) ratio of the parent fluid, due to the complex nature of As(III) uptake and possible in situ oxidation during recrystallization.

Formation of Self‐Templated 2,6‐Bis(1,2,3‐triazol‐4‐yl)pyridine [2]Catenanes by Triazolyl Hydrogen Bonding: Selective Anion Hosts for Phosphate

AbstractWe report the remarkable ability of 2,6‐bis(1,2,3‐triazol‐4‐yl)pyridine (btp) compounds 2 with appended olefin amide arms to self‐template the formation of interlocked [2]catenane structures 3 in up to 50 % yield when subjected to olefin ring‐closing metathesis in CH2Cl2. X‐ray diffraction crystallography enabled the structural characterization of both the [2]catenane 3 a and the non‐interlocked macrocycle 4 a. These [2]catenanes showed selective triazolyl hydrogen‐bonding interactions with the tetrahedral phosphate anion when screened against a range of ions; 3 a,b are the first examples of selective [2]catenane hosts for phosphate.

Formation of Self-Templated 2,6-Bis(1,2,3-triazol-4-yl)pyridine [2]Catenanes by Triazolyl Hydrogen Bonding: Selective Anion Hosts for Phosphate.

We report the remarkable ability of 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) compounds 2 with appended olefin amide arms to self-template the formation of interlocked [2]catenane structures 3 in up to 50 % yield when subjected to olefin ring-closing metathesis in CH2 Cl2 . X-ray diffraction crystallography enabled the structural characterization of both the [2]catenane 3 a and the non-interlocked macrocycle 4 a. These [2]catenanes showed selective triazolyl hydrogen-bonding interactions with the tetrahedral phosphate anion when screened against a range of ions; 3 a,b are the first examples of selective [2]catenane hosts for phosphate.

Structural analysis of molybdo-zinc-phosphate glasses: Neutron scattering, FTIR, Raman scattering, MAS NMR studies

Vitreous samples were prepared in the xMoO3–17ZnO–(83-x) NaPO3 with 35 ≥ x ≥ 55 glass forming system by energy efficient microwave heating method. Structural evolution of the vitreous network was monitored as a function of composition by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), Raman scattering, Magic Angle Spin Nuclear magnetic resonance (MAS NMR) and Neutron scattering. Addition of MoO3 to the ZnO-NaPO3 glass leads to a pronounced increase in glass transition temperature (Tg) suggesting a significant increase in network connectivity and strength. In order to analyze FTIR and Raman scattering, a simple structural model is presented to rationalize the experimental observations. A number of structural units are formed due to network modification, and the resulting glass may be characterized by a network polyhedral with different numbers of unshared corners. 31P MAS NMR confirms a clear distinction between structural species having 3, 2, 1, 0 bridging oxygens (BOs). Further, Neutron scattering studies were used to probe the structure of these glasses. The result suggests that all the investigated glasses have structures based on chains of four coordinated phosphate and six coordinated molybdate units, besides, two different lengths of P-O bonds in tetrahedral phosphate units that are assigned to bonds of the P-atom with terminal and bridging oxygen atoms.

Synthesis and characterization of the novel rare earth orthophosphates Y0.5Er0.5PO4and Y0.5Yb0.5PO4

AbstractThe new mixed rare earth (RE) orthophosphates Y0.5Er0.5PO4and Y0.5Yb0.5PO4were synthesized by a classical solid state reaction in an electrical furnace at 1200 °C. As starting materials, the corresponding rare earth oxides and diammonium hydrogen phosphate were used. The powder diffraction analyses revealed that the new compounds Y0.5Er0.5PO4and Y0.5Yb0.5PO4crystallize in a zircon-type structure being isostructural with the rare earth orthophosphate YPO4. Y0.5Er0.5PO4and Y0.5Yb0.5PO4crystallize in the tetragonal space groupI41/amd(no. 141) with four formula units in the unit cell. The structural parameters based on Rietveld refinements area= 687.27(2),c= 601.50(2) pm,V= 0.28412(1) nm3,Rp= 0.0143, andRwp= 0.0186 (all data) for Y0.5Er0.5PO4anda= 684.61(2),c= 599.31(2) pm,V= 0.28089(2) nm3,Rp= 0.0242, andRwp= 0.0313 (all data) for Y0.5Yb0.5PO4. Furthermore, the structure of Y0.5Er0.5PO4was refined from single-crystal X-ray diffraction data:a= 687.78(5),c= 601.85(4) pm,V= 0.28470(5) nm3,R1= 0.0165, andwR2= 0.0385 (all data). In both compounds, the rare earth metal ions are eightfold coordinated by oxygen atoms, forming two unique interlocking tetrahedra with two individualRE–O distances. The tetrahedral phosphate groups [PO4]3–are slightly distorted in both compounds. The individual rare earth ions share a common position (Wyckoff site 4a). The presence of two rare earth ions in the structures of the new orthophosphates Y0.5Er0.5PO4and Y0.5Yb0.5PO4was additionally confirmed by single-crystal EDX spectroscopy revealing a ratio of 1:1.