Dihydrogen Arsenate Research Articles

Local Structure and Crystallization Transformation of Hydrous Ferric Arsenate in Acidic H2O-Fe(III)-As(V)-SO42- Systems: Implications for Acid Mine Drainage and Arsenic Geochemical Cycling.

Hydrous ferric arsenate (HFA) is a common thermodynamically metastable phase in acid mine drainage (AMD). However, little is known regarding the structural forms and transformation mechanism of HFA. We investigated the local atomic structures and the crystallization transformation of HFA at various Fe(III)/As(V) ratios (2, 1, 0.5, 0.33, and 0.25) in acidic solutions (pH 1.2 and 1.8). The results show that the Fe(III)/As(V) in HFA decreases with decreasing initial Fe(III)/As(V) at acidic pHs. The degree of protonation of As(V) in HFA increases with increasing As(V) concentrations. The Fe K-edge extended X-ray absorption fine structure and X-ray absorption near-edge structure results reveal that each FeO6 is linked to more than two AsO4 in HFA precipitated at Fe(III)/As(V) < 1. Furthermore, the formation of scorodite (FeAsO4·2H2O) is greatly accelerated by decreasing the initial Fe(III)/As(V). The release of As(V) from HFA is observed during its crystallization transformation process to scorodite at Fe(III)/As(V) < 1, which is different from that at Fe(III)/As(V) ≥ 1. Scanning electron microscopy results show that Oswald ripening is responsible for the coarsening of scorodite regardless of the initial Fe(III)/As(V) or pH. Moreover, the formation of crystalline ferric dihydrogen arsenate as an intermediate phase at Fe(III)/As(V) < 1 is responsible for the enhanced transformation rate from HFA to scorodite. This work provides new insights into the local atomic structure of HFA and its crystallization transformation that may occur in AMD and has important implications for arsenic geochemical cycling.

Synthesis, crystal structure and dielectric properties of a hybrid dihydrogen arsenate salt: (C9H11N4)H2AsO4

The use of the organic aromatic amine molecule 5-amino-3-methyl-1-phenyl-1H-1,2,4-triazole to synthesize a dihydrogen arsenate hybrid salt leads to a supramolecular structure type. Single crystals of (C9H11N4)H2AsO4 were grown through slow evaporation in solution. The synthesized compound crystallizes in the monoclinic system with the non-centrosymmetric P21 space group according to the following parameters; a = 9.655 (3) Å, b = 4.7090 (15) Å, c = 14.022 (4) Å, β = 108.147 (5)° and Z = 4. The mineral part building from dihydrogen arsenate anions [H2AsO4]− is linked together and to the organic cations [C9H11N4]+ by hydrogen bonds only. The results of Hirshfeld’s analysis show that in all possible molecular contacts, the hydrogen–hydrogen and the oxygen–hydrogen are the most important interaction in the crystal (37.5 and 31.9%, respectively). The Fourier transform infrared (FT-IR) confirms the existence of vibrational modes corresponding to the organic amine molecule and mineral arsenate tetrahedron. The optimized molecular structure and the vibrational spectra were calculated by the density functional theory DFT methods and the semi-empirical PM3 calculations. Dielectric study of this compound has been measured in order to determine the electrical conductivity type giving rise to an activation energy of ΔEσ = 0.17 eV.

Theoretical investigation, of Cochran’s mode frequency, and electrical permittivity of KH2AsO4 (KDA) crystal by using Zuberav’s statistical Green function technique

Potassium dihydrogen arsenate KH2AsO4 crystal is investigated theoretically. It is an order disorder type of ferroelectrics. Another type is displacive like SrTiO3, LiNbO3, etc. The earlier model Hamiltonian (PLCM) is modified by adding some extra terms into it. Applying two time thermal dependent statistical Green function technique employing modified model, formulae for, Cochran’s mode frequency, electrical permittivity, Curie temperature, tangent delta, shift and width, are derived for the potassium dihydrogen arsenate crystal. Model values are fitted for KH2AsO4 crystal to obtain variation with temperature. Results are compared with experimental variations shown by Kaminow et al. [4] for the alkali phosphate potassium dihydrogen arsenate KH2AsO4 crystal.

Theoretical investigation of ferroelectric phase transition, and tangent delta in CsH2AsO4 (CDA) crystal

In this present work, Cesium Dihydrogen Arsenate of ordered dis-ordered type H-bonded crystal is theoretically investigated. Presently modified Pseudo Spin Lattice Coupled Mode (PLCM) model by adding some extra terms, like direct spin–spin terms, third-order and fourth-order phonon anharmonic terms, and extra spin–lattice terms. By using the Green function approach and Dyson’s equation, formulae for various quantities are find out. Thermal variations of Cochran’s mode frequency, electrical permittivity, phase transition, tangent delta, shift, and width are obtained for Cesium Dihydrogen Arsenate crystal. A comparison with theoretical findings has been made with the experimental finding reported by Blinc et al. [8]. A good agreement is seen.

Study of Ferroelectric Properties of Hydrogen Bonded Rubidium Dihydrogen Arsenate (RdA) Crystal

A simple pseudospin lattice coupled mode model with addition of third and fourth-order phonon anharmonic interactions terms, direct spin-spin interactions terms and external electric field term has been considered for investigation of transition phenomena and dielectric properties of hydrogen bonded ferroelectric crystal Rubidium dihydrogen arsenate (RDA). A double-time thermal dependent Green’s function method has been used for derivation of response function. From response function shift, width and soft mode frequency have been derived for RDA crystal. Response function is also related to dielectric constant which has been obtained in present paper. By fitting model values of different parameters in obtained expressions, the temperature variations of normal mode frequency, dielectric constant, and loss tangent have been calculated numerically for RDA crystal. Our theoretical results are compared with experimental results. It is observed that our theoretical results agree with experimental results. Therefore, it can be concluded that the modified pseudo-spin lattice coupled mode model with the simplest approximation is quite suitable to explain the transition and dielectric properties of RDA crystal.

Temperature dependence of dielectric properties in Potassium dihydrogen arsenate crystal

Potassium Dihydrogen Arsenate (KH2AsO4, KDA) is an inorganic arsenate ferroelectric crystal which is a KDP-family member and undergoes a ferroelectric phase transition at 96 K. A simple pseudospin lattice coupled mode model (PLCM) with some higher order terms like direct spin–spin interaction, third and fourth-order phonon anharmonic interaction terms and external electric field term, with two-time temperature dependent Green’s function technique has been employed for the evaluation of expression of response function. We can obtain and calculate soft mode frequency (Ω^), Dielectric constant (ε), and loss tangent (tanδ) expressions from response function for KDA crystal. We have shown temperature dependence of soft mode frequency (Ω^), Dielectric constant (ε), and loss tangent (tanδ) in Figs. 1-3. We have compared our findings, which seemed to be in fair alignment with experimental evidence.

Size-Selective Urea-Containing Metal-Organic Frameworks as Receptors for Anions.

Anion recognition by neutral hosts that function in aqueous solution is an emerging area of interest in supramolecular chemistry. The design of neutral architectures for anion recognition still remains a challenge. Among neutral anion receptor systems, urea and its derivatives are considered as "privileged groups" in supramolecular anion recognition, since they have two proximate polarized N-H bonds exploitable for anion recognition. Despite promising advancements in urea-based structures, the strong hydrogen bond drives detrimental self-association. Therefore, immobilizing urea fragments onto the rigid structures of a metal-organic framework (MOF) would prevent this self-association and promote hydrogen-bond-accepting substrate recognition. With this aim, we have synthesized two new urea-containing metal-organic frameworks, namely [Zn(bpdc)(L2)]n·nDMF (TMU-67) and [Zn2(bdc)2(L2)2]n·2nDMF (TMU-68) (bpdc = biphenyl-4,4'-dicarboxylate; bdc = terephthalate; L2 = 1,3-bis(pyridin-4-yl)urea), and we have assessed their recognition ability toward different anions in water. The two MOFs show good water stability and anion affinity, with a particular selectivity toward dihydrogen arsenate for TMU-67 and toward fluoride for TMU-68. Crystal structure characterizations reveal 3-fold and 2-fold interpenetrated 3D networks for TMU-67 and TMU-68, respectively, where all single interpenetrated networks are hydrogen bonded to each other in both cases. Despite the absence of self-quenching, the N-H urea bonds are tightly hydrogen bonded to the oxygen atoms of the dicarboxylate ligands and cannot be directly involved in the recognition process. The good performance in anion sensing and selectivity of the two MOFs can be ascribed to the network interpenetration that, shaping the void, creates monodimensional channels, decorated by exposed oxygen atom sites selective for arsenate sensing in TMU-67 and isolated cavities, covered by phenyl groups selective for fluoride recognition in TMU-68.

Three new acid M+ arsenates and phosphates with multiply protonated As/PO4 groups.

The crystal structures of caesium dihydrogen arsenate(V) bis[trihydrogen arsenate(V)], Cs(H2AsO4)(H3AsO4)2, ammonium dihydrogen arsenate(V) trihydrogen arsenate(V), NH4(H2AsO4)(H3AsO4), and dilithium bis(dihydrogen phosphate), Li2(H2PO4)2, were solved from single-crystal X-ray diffraction data. NH4(H2AsO4)(H3AsO4), which was hydrothermally synthesized (T = 493 K), is homeotypic with Rb(H2AsO4)(H3AsO4), while Cs(H2AsO4)(H3AsO4)2 crystallizes in a novel structure type and Li2(H2PO4)2 represents a new polymorph of this composition. The Cs and Li compounds grew at room temperature from highly acidic aqueous solutions. Li2(H2PO4)2 forms a three-dimensional (3D) framework of PO4 tetrahedra sharing corners with Li2O6 dimers built of edge-sharing LiO4 groups, which is reinforced by hydrogen bonds. The two arsenate compounds are characterized by a 3D network of AsO4 groups that are connected solely via multiple strong hydrogen bonds. A statistical evaluation of the As-O bond lengths in singly, doubly and triply protonated AsO4 groups gave average values of 1.70 (2) Å for 199 As-OH bonds, 1.728 (19) Å for As-OH bonds in HAsO4 groups, 1.714 (12) Å for As-OH bonds in H2AsO4 groups and 1.694 (16) Å for As-OH bonds in H3AsO4 groups, and a grand mean value of 1.667 (18) Å for As-O bonds to nonprotonated O atoms.

Adsorption of hydrogen arsenate and dihydrogen arsenate ions from neutral water by UiO-66-NH2

The metal-organic framework (MOF) UiO-66-NH2 was synthesized with different substrate to solvent ratios and its morphology, surface area, pore distributions, and NMR, XRD, and TGA-FTIR patterns were obtained. Adsorption tests at pH 7 and 25 °C showed that the produced UiO-66-NH2 has a hydrogen arsenate adsorption capacity of 76.9 mg/g. With the affinity onto Zr clusters, this MOF also can adsorb phosphate ions from water. Treatment with 1–4 M hydrochloric acid (HCl) protonated the amine groups in the MOF. Treatment with 1 M HCl at 25 °C for 6 h maximized the adsorption capacity of UiO-66-NH2 to 161.3 mg/g, such that the protonated amine groups accounted for 53.7% of the adsorption of arsenate from the water. The use of excessively strong acid at elevated temperature reduced the adsorption capacity.

Crystallographic and computational studies of a new organoarsenate compound: o-anisidinium dihydroarsenate.

The crystal structure and the results of theoretical calculations for the new organoarsenate salt o-anisidinium dihydroarsenate (systematic name: 2-methoxyanilinium dihydrogen arsenate), C7H10NO+·H2AsO4-, are reported. The salt, crystallizing in the triclinic space group P-1, was synthesized using a solution method and was characterized by single-crystal X-ray diffraction analysis. It possesses a layered supramolecular architecture in the crystal. The intermolecular interactions were studied using Hirshfeld surface analysis which confirmed that hydrogen bonds and H...H contacts play dominant roles in the crystal structure of the investigated system. An analysis of the electronic structure and molecular modelling using charge distribution confirms the good electrophilic reactivity of the title compound.

Crystal structure of sodium di-hydrogen arsenate.

Single crystals of the title compound, Na(H2AsO4), were obtained by partial neutralization of arsenic acid with sodium hydroxide in aqueous solution. The crystal structure of Na(H2AsO4) is isotypic with the phosphate analogue and the asymmetric unit consists of two sodium cations and two tetra-hedral H2AsO4- anions. Each of the sodium cations is surrounded by six O atoms of five H2AsO4- groups, defining distorted octa-hedral coordination spheres. In the extended structure, the sodium cations and di-hydrogen arsenate anions are arranged in the form of layers lying parallel to (010). Strong hydrogen bonds [range of O⋯O distances 2.500 (3)-2.643 (3) Å] between adjacent H2AsO4- anions are observed within and perpendicular to the layers. The isotypic structure of Na(H2PO4) is comparatively discussed.

M3+(H2AsO4)(H2As2O7) (M3+= Al, Ga) and In2(H2AsO4)2(H2As2O7)2: a new layer structure type and a new framework structure type containing the rare H2As2O72−group

The crystal structures of hydrothermally synthesized aluminium dihydrogen arsenate(V) dihydrogen diarsenate(V), Al(H2AsO4)(H2As2O7), gallium dihydrogen arsenate(V) dihydrogen diarsenate(V), Ga(H2AsO4)(H2As2O7), and diindium bis[dihydrogen arsenate(V)] bis[dihydrogen diarsenate(V)], In2(H2AsO4)2(H2As2O7)2, were determined from single-crystal X-ray diffraction data collected at room temperature. The first two compounds are representatives of a novel sheet structure type, whereas the third compound crystallizes in a novel framework structure. In all three structures, the basic building units are M3+O6 octahedra (M = Al, Ga, In) that are connected via one H2AsO4- and two H2As2O72- groups into chains, and further via H2As2O72- groups into layers. In Al/Ga(H2AsO4)(H2As2O7), these layers are interconnected by weak-to-medium-strong hydrogen bonds. In In2(H2AsO4)2(H2As2O7)2, the H2As2O72- groups link the chains in three dimensions, thus creating a framework topology, which is reinforced by weak-to-medium-strong hydrogen bonds. The three title arsenates represent the first compounds containing both H2AsO4- and H2As2O72- groups.

Growth, morphology, structure and characterization ofL-histidinium dihydrogen arsenate orthoarsenic acid single crystal

L-Histidinium dihydrogen arsenate orthoarsenic acid (LHAS) crystals were grown by the slow evaporation method. Single-crystal X-ray diffraction confirms monoclinic structure. The growth rates of various planes of LHAS crystals were estimated by morphological study. Hirshfeld surface and fingerprint plots were analyzed to investigate the intermolecular interactions at 0.002 a.u. present in the crystal structure. The functional groups and phase behavior of the compound are studied by FTIR spectroscopy and differential scanning calorimetry (DSC). A ferroelectric to paraelectric phase transition at 307 K was observed in dielectric studies. The piezoelectric charge coefficients of the grown crystal were found to be 2 pC/N. The values of coercive field (Ec), remnant polarization (Pr) and spontaneous polarization (Ps) in the hysteresis loop are found to be 5.236 kV cm(-1), 0.654 µC cm(-2) and 2.841 µC cm(-2), respectively. Piezoelectricity and ferroelectricity are reported for the first time in LHAS crystals. The mechanical strength was confirmed from microhardness study and void volume. Due to the low value of the dielectric constant, and good piezoelectric and ferroelectric properties, LHAS crystals can be used in microelectronics, sensors and advanced electronic devices.

Synthesis, spectroscopic studies and crystal structure of (Et4N)(SnMe3)(7)(HASO(4))(4) center dot 2H(2)O

On allowing tetraethylammonium dihydrogen arsenate dihydrate to react with trimethyltin chloride, the title compound has been obtained and characterized by infrared, Mossbauer and NMR techniques. Its crystal structure has been determined and consists of layers containing both corner sharing AsO4H tetrahedra and trans-O2SnC3 entities. It contains large cavities in which tetraethylamonium cations are located. (C) 2004 Elsevier B.V. All rights reserved.

Toxicity of Arsenic to Photobacterium phosphoreum, Daphnia magna, and Danio rerio at Different pH Levels

Although it has been widely known that arsenic poses great threat to organisms and arsenic species account for the toxic effect of the metalloid, relatively little attention has been given to the arsenic toxicity to different organisms at different pH values. Three kinds of aquatic organisms including Photobacterium phosphoreum, Daphnia magna, and Danio rerio were used to study the effects of pH on the toxicity of arsenic. Toxicity test results were analyzed by calculating EC50 values and for arsenic species at five different pH values (5.0, 6.0, 7.0, 8.0, and 9.0). As a result, As(III) is more toxic to the tested organisms than As(V), and P. phosphoreum was more sensitive to the toxicity of arsenic than D. magna and D. rerio. The toxicity of As(III) species is different for different organisms: dihydrogen arsenite, H2AsO3–, is more toxic to P. phosphoreum and D. rerio than arsenous acid, H3AsO3, while H3AsO3 is more toxic to D. magna. As for As(V), arsenate, HAsO42−, is the most toxic to P. phosphoreum, whereas dihydrogen arsenate, H2AsO4–, may be responsible for the toxicity to D. magna and D. rerio. As(III) and As(V) are more toxic to P. phosphoreum in an alkaline environment, while for D. magna in an acidic environment and As(III) is more toxic to D. rerio in an alkaline environment and As(V) in an acidic environment.

Crystal Structure, Thermal Analysis, IR and Raman Spectroscopic Investigations of (C8H22N2)(AsO2(OH)2)2

Chemical preparation, X-ray single crystal, thermal analysis, IR and Raman spectroscopic investigations of (C8H22N2)(AsO2(OH)2)2 are described. The 2-(diisopropyl ammonium)ethylammonium-bis-(dihydrogen arsenate) crystallizes in the orthorhombic system with P212121 space group. The unit cell dimensions are a = 8.3009(2) A, b = 8.5640(3) A, c = 23.1480(7) A with V = 1645.57(9) A3 and Z = 4. The structure was solved using direct method and refined to a reliability R factor of 4.37 %. The (C8H22N2)(AsO2(OH)2)2 structure provides a new interesting example of infinite inorganic layers of [H2AsO4] n n− where the arsenate groups are interconnected by O–H···O hydrogen bonds. The crystal structure can be described as infinite layers centered by planes (110). Thermal analysis reveals the anhydrous character of the compound. IR and Raman spectra are reported and discussed on the basis of group theoretical analysis.

Re-evaluation of the Thermodynamic Activity Quantities in Aqueous Solutions of Silver Nitrate, Alkali Metal Fluorides and Nitrites, and Dihydrogen Phosphate, Dihydrogen Arsenate, and Thiocyanate Salts with Sodium and Potassium Ions at 25 °C

The Huckel equation used in this study to correlate the experimental activities of dilute solutions of silver nitrate, alkali metal fluorides, and sodium and potassium salts with dihydrogen phosphate, dihydrogen arsenate, and thiocyanate ions up to a molality of about 1.5 mol·kg−1 contains two parameters being dependent on the electrolyte: B [that is related closely to the ion-size parameter (a*) in the Debye−Huckel equation] and b1 (this parameter is the coefficient of the linear term with respect to the molality, and this coefficient is related to hydration numbers of the ions of the electrolyte). In more concentrated solutions of these electrolytes and of alkali metal nitrites in the best case up to a molality of 10 mol·kg−1, an extended Huckel equation was used; it contains additionally a quadratic term with respect to the molality, and the coefficient of this term is the parameter b2. All parameter values for the Huckel equations of AgNO3 solutions were determined from the isopiestic data measured by...

Band Structure and Optical Characteristics of TDA Crystals

The electronic band structure and related electric and optical properties of the Tris(hydroxymethyl)aminomethane(Dihydrogen)Arsenate crystal (TDA) have been studied within the density functional theory using the ab-initio codes CASTEP, CRYSTAL and ABINIT. On the basis of the dielectric functions obtained ϵ1i (ω) (i = x, y, z), the phase matching angles for second harmonic generation have been calculated, which indicate possibility of this effect in TDA in the photon energy range 0.5–0.75 eV. The dependence of electrical polarization on the crystal unit cell volume has been calculated and the results obtained are discussed in connection with pyroelectric effect in TDA.

Crystal Structure of La3OBr[AsO3]2

Colorless needles of the arsenite bromide La3OBr[AsO3]2 were synthesized from ammonium dihydrogen arsenate, ammonium bromide and lanthanum oxide in an NaBr/KBr flux at 900 °C. La3OBr[AsO3]2 crystallizes with the centrosymmetric tetragonal La3OCl[AsO3]2 type, space group P42/mnm. The structure was refined from single-crystal diffractometer data: a = 13.0431(15), c = 5.6127(7) Å , wR2 = 0.0454, 945 F2 values, and 39 variables. It consists of chains of trans-edge-sharing OLa4/2 tetrahedra which are coordinated by [AsO3]3− units via the oxygen atoms

No evidence for Evans’ holes in the A, B, C vibrational structure of potassium dihydrogen arsenate

We have used inelastic neutron scattering (INS) spectroscopy to study the "A, B, C" region of the hydrogen bond in potassium dihydrogen arsenate. The broad spectral feature observed in infrared spectroscopy is shown to be associated with a ridge of constant intensity in the INS, which follows the recoil line for a unit-mass particle. The onset energy of the ridge is unclear but, we believe, is associated with the optical "C" feature at 1610 cm(-1), and which we assign to nu(O-H). The "B" and "A" optical bands were both demonstrated to be two-quantum events and are, thus, not associated with the fundamental nu(O-H). They are readily assigned to the harmonic overtone delta(OH)(0-2) and the combination gamma(OH)(0-1)+delta(OH)(0-1), which both sit astride the ridge and there is no evidence for Evans' holes. The other overtone, gamma(OH)(0-2), has been assigned to a very weak feature, observed for the first time at 1900 cm(-1). A simple model was used to describe the intensity distributions.