Phosphate Tetrahedra Research Articles

Neutron powder diffraction studies of silicon-substituted hydroxyapatite

The incorporation of a small amount of silicon in the hydroxyapatite (HAp) lattice is known to improve the bioactivity of the material. The effect of silicon substitution was studied by comparing samples of pure and 0.4 wt% silicon-substituted HAp prepared by an aqueous precipitation method. High-resolution neutron powder diffraction and Rietveld refinement methods were used to investigate the effect of silicon substitution on the crystal structure parameters of the HAp lattice from room temperature down to 20 K. Small structural changes in the lattice constants, interatomic distances, site occupancies and distortion of the phosphate tetrahedron were found. Modifications of the Fourier transform infrared spectra as well as appearance of new modes were observed in the silicon-substituted sample. Heat treatment and silicon substitution also affected the morphology and crystallinity of this bioapatite.

Organically Templated Mixed‐Valent Iron Sulfates Possessing Kagome and Other Types of Layered Networks.

AbstractFor Abstract see ChemInform Abstract in Full Text.

THE CRYSTAL STRUCTURE OF BERGENITE, A NEW GEOMETRICAL ISOMER OF THE PHOSPHURANYLITE GROUP

The crystal structure of bergenite, ideally Ca2Ba4[(UO2)3O2(PO4)2]3(H2O)16, monoclinic, space group P21/c, a 10.092(1), b 17.245(2), c 17.355(2) A, 113.678(2)°, V 2766.2(3) A 3 , Z = 2, Dcalc 4.82 g/cm 3 , was solved by direct methods and refined by full-matrix least-squares techniques on the basis of F 2 to agreement indices R1 of 5.0% calculated for 4118 unique observed reflections (|Fo| ≥ 4F), and wR2 of 11.9% for all data. Intensity data were collected at room temperature using MoK radiation and a CCD-based area detector. The structure of bergenite contains five symmetrically independent uranium atoms, each of which is part of a (UO2) 2+ uranyl ion. The uranyl ions of U(1), U(2) and U(3) are coordinated by five additional ligands giving pentagonal bipyramids, and the uranyl ions of U(4) and U(5) are coordinated by six additional ligands yielding hexagonal bipyramids. The uranyl pentagonal bipyramids share edges, forming dimers, which are linked to uranyl hexagonal bipyramids on either side, resulting in chains of bipyramids. Each uranyl hexagonal bipyramid shares two equatorial edges with phosphate tetrahedra, and the resulting uranyl phosphate chains are linked into sheets by the sharing of vertices of phosphate tetrahedra with uranyl pentagonal bipyramids of adjacent chains. The uranyl phosphate sheet in bergenite is a new geometrical isomer of the phosphuranylite group; the phosphate tetrahedra between the uranyl chains vary orientations in an up-up-down up-up-down (uuduud) pattern, and the pairs of tetrahedra attached to uranyl hexagonal bipyramids change orientations in a complementary same-same-opposite (SSO) manner (symbol uuduudSSO). In bergenite, the uranyl phosphate sheets are oriented parallel to (¯ and the interlayer contains one calcium atom, two barium atoms and eight symmetrically distinct H2O groups.

The crystal structure of synthetic autunite, Ca[(UO2)(PO4)]2(H2O)11

Autunite, Ca[(UO2)(PO4)]2(H2O)11, is amongst the most abundant and widely distributed of the uranyl phosphate minerals, yet because of its pseudo-tetragonal symmetry and rapid dehydration in air, the details of its symmetry, stoichiometry, and structure were previously uncertain. The crystal structure of synthetic autunite was solved by direct methods and refined by full-matrix least-squares techniques to agreement indices R1 = 0.041, calculated for the 1497 unique observed reflections (|F0| ≥ 4σF), and wR2 = 0.119 for all data. Autunite is orthorhombic, space group Pnma, Z = 4, a = 14.0135(6), b = 20.7121(8), c = 6.9959(3) Å, V = 2030.55(15) Å3. The structure contains the wellknown autunite type sheet with composition [(UO2)(PO-)]-, resulting from the sharing of equatorial vertices of the uranyl square bipyramids with the phosphate tetrahedra. The calcium atom in the interlayer is coordinated by seven H2O groups and two longer distances to uranyl apical O atoms. Two symmetrically independent H2O groups are held in the structure only by hydrogen bonding. Bond-length-constrained refinement provided a crystal-chemically reasonable description of the hydrogen bonding.

The structure and properties of binary zinc phosphate glasses studied by molecular dynamics simulations

In recent years, the use of molecular dynamics (MD) simulations to understand and predict the properties of materials has become an increasingly popular and powerful tool. In this study, MD simulations were used to investigate the structural and physical properties of a binary zinc phosphate glass series, xZnO · (100− x)P 2O 5, (40⩽ x⩽70) where x is the mole percent modifier. A newly developed forcefield model incorporating Coulombic, plus two- and three-body interactions was employed, with the model parameters being empirically derived from known zinc–phosphate crystal structures. This zinc–phosphate forcefield model was used to perform MD calculations of densities, glass transition temperatures, T g, average coordination numbers (CN) radial distribution functions, G( r), and pair distribution function, g( r), as a function of Zn concentration. In addition, the effects of computational quenching rates on the simulated densities were also investigated. Overall, the MD simulation results revealed the presence of long-range order in the form of rings and chains near the metaphosphate composition. These extended range structures disappeared beyond the metaphosphate composition, becoming isolated non-bridging phosphate tetrahedron as the Zn concentration approached the pyrophosphate composition. The MD simulations also revealed that the average Zn CN was invariant across the entire Zn concentration range investigated. These results demonstrate that the observed T g behavior does not require an increase in the Zn CN.

Determination and Rietveld refinement of the crystal structure of Li0.50Ni0.25TiO(PO4) from powder X-ray and neutron diffraction

The structure of the oxyphosphate Li0.50Ni0.25TiO(PO4) has been determined from conventional X-ray and neutron powder diffraction data. The parameters of the monoclinic cell (space group P21/c, Z=4), obtained from X-ray results, are: a=6.3954(6) Å, b=7.2599(6) Å, c=7.3700(5) Å, and β=90.266(6)°; those resulting from neutron study are: a=6.3906(7) Å, b=7.2568(7) Å, c=7.3673(9) Å, and β=90.234(7)°. Refinement by the Rietveld method using whole profile, leads to satisfactory reliability factors: cRwp=0.128, cRp=0.100, and RB=0.038 for X-ray and cRwp=0.110, cRp=0.120, and RB=0.060 for neutrons. The structure of Li0.50Ni0.25TiO(PO4) can be described as a TiOPO4 framework constituted by chains of tilted corner-sharing TiO6 octahedra running parallel to the c axis and cross linked by phosphate tetrahedra. In this framework, there are octahedral cavities occupied by Li and Ni atoms: Li occupies the totality of the 2a sites and Ni occupies statistically half of the 2b sites. Ti atoms are displaced from the center of octahedra units in alternating long (2.242 Å) and short (1.711 Å) Ti–O bonds along chains.

Crystal structure of dilithium indium (monophosphate-monohydrogenmonophosphate), Li2In[(PO4)(HPO4)

HInLi2O8P2, monoclinic, P121/n1 (No. 14), a = 4.8345(7) A, b = 8.236(1) A, c = 7.728(1) A, = 103.466(7)°, V = 299.2 A, Z = 2, Rgt(F) = 0.022, wRref(F) = 0.060, T = 295 K. Source of material Li2In[(PO4)(HPO4)] was obtained during borophosphate synthesis under mild hydrothermal conditions. The reaction was carried out with a mixture of In (0.574 g, dissolved in 3 ml 37% HCl), LiH2PO4 (10.393 g), and Li2B4O7 (1.691 g) with the molar ratio of 1 : 20 : 2. The mixture was filled in a 20 ml teflon autoclave with a filling degree of about 50%. Autoclaves were placed in an oven with subsequent heating at 443 K for 7 days. All starting materials were of analytical grade and used without further purification. The composition of the product was confirmed by chemical analysis (ICP) with Li : In : P : O : H = 1.96 : 0.93 : 2 : 7.5 : 1.3. Experimental details The hydrogen position could not be located from difference Fourier analysis, maybe because of affection of the heavy atom indium. Therefore, the position of the hydrogen atom in the isotypic compound Li2Fe[(PO4)(HPO4)] [3] was assumed for the title compound and maintained constant in the refinement. Discussion Only two lithium indium phosphates (LiInP2O7, Li3In2(PO4)3) [1,2] have been reported up to now. Here we report on the first acid lithium indium phosphate containing a HPO4-group. The crystal structure of the title compound is characterized by isolated InO6 octahedra which share common O-atoms with adjacent PO4 tetrahedra to form a three-dimensional network structure. Each PO4 tetrahedron shares common O-corners with three neighboring InO6 octahedra. As mentioned above, by analogy to the isotypic phase Li2Fe[(PO4)(HPO4)], the H atom was assumed to be disordered and in an ordered model O3PO···H–OPO3 groups would exist. The crystal structure contains eight-membered rings formed by alternating InO6 octahedra (4×) and phosphate tetrahedra (4×). Lithium cations are located within channels formed by the eight-membered rings running along the a axis. Within the channels, each eight-membered ring is divided by the O···H–O bridges. In—O bond distances in the InO6-octahedron range from 2.129 A to 2.147 A. Each Li atom is coordinated by 4 oxygen atoms with bond distances d(Li—O) = 1.951 A – 2.047 A. Bond lengths and angles of the phosphate tetrahedra are reflecting those in other phosphates [1,2]. Z. Kristallogr. NCS 217 (2002)307-308 307 © by Oldenbourg Wissenschaftsverlag, Munchen Crystal: colorless isometric fragment of 0.10 mm diameter Wavelength: Mo K radiation (0.71073 A) : 44.88 cm−1 Diffractometer, scan mode: Rigaku AFC7-CCD, 400 images, = 0.6° scan, = 0.6°, 2 max: 59.78° N(hkl)measured, N(hkl)unique: 4423, 732 Criterion for Iobs, N(hkl)gt: Iobs > 2 (Iobs), 694 N(param)refined: 62 Programs: SIR92 [4], SHELXL-97 [5], DIAMOND [6] Table 1. Data collection and handling. H(1) 4e 0.50 0.571 0.519 0.518 0.05 Table 2. Atomic coordinates and displacement parameters (in A). Atom Site Occ. x y z Uiso

Crystal structure of diammonium indium (monophosphate-monohydrogenmonophosphate), (NH4)2ln[(PO4)(HPO4)

H9InN2O8P2, orthorhombic, Fdd2 (No. 43), a = 17.459(4) A, b = 9.200(2) A, c = 9.720(2) A, V = 1561.3 A, Z = 8, Rgt(F) = 0.061, wRref(F) = 0.148, T = 295 K. Source of material (NH4)2In[(PO4)(HPO4)] was synthesized under mild hydrothermal conditions. The reactions were carried out with mixtures of InCl3, H3BO3 and (NH4)H2PO4 with the molar ratio of 1:6 : 8 in aqueous solution. The mixture was sealed in 20 ml glass tubes. The filling of the solution were about 30% of the glass tubes. The glass tubes were placed in an oven with subsequent heating at 413 K for 7 days. All starting materials were of analytical grade and used without further purification. Discussion There were only two ammonium-indium phosphates [1,2] and one ammonium-indium borophospahte [3] reported up to now and the title compound is another indium phosphate with ammonium cation. The title compound has a new structure type which is characterized by isolated InO6 octahedra sharing common O-corners with six isolated PO4 tetrahedra to form a three dimensional network structure. Each PO4 tetrahedron shares common O-corners with three InO6 octahedra. According to the present model, the hydrogen atom bridges symmetrically two PO4 tetrahedra. However, the H atom is presumably disordered, splitting in two positions, and in an ordered model the O3PO···H–OPO3 groups would exist. The structure can also be considered as a packing of layers perpendicular to the a-axis. Each layer is constructed by fusing eight-membered rings formed by four InO6 octahedra and four phosphate (or hydrogenphosphate) tetrahedra. The alternating layers are shifted by 1/4 of a period along both band c-axis with respect to their neighboring layers. This construction results to two sets of channels runing along the [011] and [011] directions. The channels have a nearly rectangular cross section and are formed by two five-membered U-shaped half-rings in an up-and-down fashion. The ammonium groups are distributed within the channels. The In—O bond distances within the InO6 octahedron range from 2.093 A to 2.171 A. Bond lengths and angles in the phosphate PO4 tetrahedra are similar to those in other phosphates. Z. Kristallogr. NCS 217 (2002)309-310 309 © by Oldenbourg Wissenschaftsverlag, Munchen Crystal: colorless prism, size 0.07 × 0.07 × 0.10 mm Wavelength: Mo K radiation (0.71073 A) : 34.61 cm−1 Diffractometer, scan mode: Enraf Nonius CAD4, /2 2 max: 67.74° N(hkl)measured, N(hkl)unique: 834, 834 Criterion for Iobs, N(hkl)gt: Iobs > 2 (Iobs), 644 N(param)refined: 57 Programs: SIR92 [4], SHELXL-97 [5], DIAMOND [6] Table 1. Data collection and handling. O(1) 16b 0.2476(7) 0.423(1) 0.496(1) 0.013(2) O(2) 16b 0.2476(7) 0.594(1) 0.689(1) 0.009(2) O(3) 16b 0.1205(5) 0.518(1) 0.583(1) 0.013(2) O(4) 16b 0.1962(6) 0.340(1) 0.726(1) 0.015(2) N(1) 16b 0.1439(9) 0.824(2) 0.499(2) 0.024(3) H(1) 8a 1/4 1/4 0.7135 0.05 H(2) 16b 0.1879 0.8895 0.5567 0.05 H(3) 16b 0.1486 0.8201 0.4136 0.05 H(4) 16b 0.0885 0.8504 0.5257 0.05 H(5) 16b 0.1694 0.7424 0.5515 0.05 Table 2. Atomic coordinates and displacement parameters (in A). Atom Site x y z Uiso

Synthesis and Structure of the New Ammonium Indium Phosphate (NH4)In(OH)PO4

A new ammonium indium phosphate (NH4)In(OH)PO4 was prepared by hydrothermal reaction in the In2O3–NH4H2PO4–NH3/OH system (T=200°C, autogenous pressure, 7 days). The formula (NH4)In(OH)PO4 was determined on the basis of chemical and thermal analysis (TG/DSC), X-ray powder diffraction and IR-spectroscopy. (NH4)In(OH)PO4 crystallizes in the tetragonal system with space group P43212 (No. 96); a=9.4232(1) Å, c=11.1766(1) Å, V=992.45(2) Å3; Z=8. The crystal structure was refined by the Rietveld method (Rw=6.35%, Rp=5.10%). The second-harmonic generation study confirmed that structure of (NH4)In(OH)PO4 does not have a center of symmetry. The cis-InO4(OH)2 octahedra form helical chains, parallel to the c-axis. The In–O–In bonds are nearly equidistant. The chains are interconnected by phosphate tetrahedra and create tunnels containing the NH4+ ions along the c-axis. (NH4)In(OH)PO4 is isostructural with RbIn(OH)PO4.

Synthesis and Characterization of New Lamellar Templated Titanium(IV) Phosphates with Perforated Layers: MIL-28n or Ti3O2X2(HPO4)x(PO4)y·(N2CnH2n+6)z·(H2O)2 (n = 2, 3; x = 0, 2; y = 4, 2; z = 3, 2; X = F, OH)

The title compounds (MIL-28 n ) were prepared hydrothermally (3-4 days, 453-473 K, autogenous pressure) in the presence of organic bases (NH 2 -(CH 2 ) n -NH 2 (n = 2, 3)). The structure of MIL-28 3 or [Ti 3 O 2 (OH) 2 (HPO 4 ) 2 (PO 4 ) 2 ].(NH 3 -(CH 2 ) 3 -NH 3 ) 2 .(H 2 O) 2 has been determined ab initio from powder diffraction data and was refined in the orthorhombic space group Fm2m (no. 42). Its unit cell is a = 18.331(2) A, b = 18.943(3) A, c = 7.111(1) A, V = 2469.2(2) A 3 , z = 4. MIL-28 3 is two-dimensional. Its inorganic layers are made of trans-linked corner-sharing TiO 6 octahedra chains connected with tetrahedral phosphate groups and related via isolated TiO 4 (OH) 2 octahedra. This creates 10-member-ring apertures within the inorganic layers in which diamine molecules are present. Both water molecules, located in the interlayer space, and organic agents interact with terminal OH groups and ensure the stability of the structure. MIL-28 2 or [Ti 3 O 2 F 2 (PO 4 ) 4 ].(NH3-(CH 2 ) 2 -NH 3 ) 3 .(H 2 O) 2 crystallizes in a triclinic space group (P1 (no. 1)) with the following parameters: a = 10.071(5) A, b = 18.920(2) A, c = 7.107(4), a = 89.88(2), β = 106.23(2)°, y = 100.45(1)°, and V = 1273.5-(3) A 3 . Although the structure of compound MIL-28 2 has not been determined, a brief study will show that it shares strong features with those of MIL-28 3 .

The Crystal Structure of Triuranyl Diphosphate Tetrahydrate

The hydrated neutral uranyl phosphate, (UO2)3(PO4)2(H2O)4, was synthesized by hydrothermal methods. Intensity data were collected using MoKα radiation and a CCD-based area detector. The crystal structure was solved by direct methods and refined by full-matrix least-squares techniques to agreement indices wR2=0.116 for all data, and R1=0.040, calculated for the 2764 unique observed reflections (∣Fo∣≥4σF). The compound is orthorhombic, space group Pnma, Z=4, a=7.063(1) Å, b=17.022(3) Å, c=13.172(3) Å, V=1583.5(5) Å3. The structure consists of sheets of phosphate tetrahedra and uranyl pentagonal bipyramids, with composition [(UO2)(PO4)]− and the uranophane sheet anion topology. The sheets are connected by a uranyl pentagonal bipyramid in the interlayer that shares corners with a phosphate tetrahedron on each of two adjacent sheets, resulting in an open framework with isolated H2O groups in the larger cavities of the structure.

Infrared spectroscopic studies of ion-conducting silver phosphate glasses doped with zinc and cadmium halides

Silver phosphate glassed doped with different concentrations of zinc and cadmium halides have been prepared and characterized by using X-ray diffraction, elemental analyses, DSC studies, ion transport and infrared spectral studies. FTIR spectra of all the samples were done which indicate the presence of characteristic P  O  P linkages of linear polyphosphate chain and two non-bridging oxygen atoms bonded to phosphorus atoms (O  P  O units) in the phosphate tetrahedra. On the basis of IR studies, a plausible resonance chain structure for these glasses has been established and discussed.

Crystal Structures of Na2ZnP2O7, K2ZnP2O7, and LiKZnP2O7 Phases in the M2O–ZnO–P2O5 Glass-Forming System (M = Li, Na, and K)

The crystal structures of Na2ZnP2O7 and K2ZnP2O7 are determined from X-ray powder diffraction data. The structure of LiKZnP2O7 is determined using a single-crystal sample. In the alkali zinc phosphates studied, the Zn2+ cation is coordinated by four oxygen atoms of the phosphate tetrahedra. In the first two compounds, the [ZnP2O7]2– anion has the form of a sheet consisting of Zn and P oxygen-containing tetrahedra that involves only five-membered rings. In the LiKZnP2O7 structure, the zinc phosphate anion of the same composition has the form of a three-dimensional skeleton with a three-dimensional system of channels. These channels are linked via six-membered, eight-membered, and ten-membered rings. The atomic coordinates and interatomic distances are reported.

Comparison of crystal structure parameters of natural and synthetic apatites from neutron powder diffraction

A systematic behavior in the crystal structure parameters of natural, synthetic, carbonate, and non-carbonate apatite is revealed from Rietveld refinements of neutron powder diffraction experiments. The results of this work on synthetic carbonate hydroxyapatites (CHAps) are consistent with the mechanism of carbonate substitution on the mirror plane of the phosphate tetrahedron, as it was introduced for the natural carbonate fluorapatite (CFAp). The present comparison shows that the tetrahedral bond lengths P–O1 and P–O2 decrease by 3–4% in all carbonate apatites. The atomic displacement parameters (ADPs) of the tetrahedral (T) and the O3 sites are greater in the carbonate than in the non-carbonate apatites. The atomic positional disorder of the T site (P/C site) is greater in the CFAp than in the CHAps, while the opposite happens at the O3 sites. Finally, the room-temperature ADPs of all of the atoms in the CFAp and CHAps show the same behavior as in the corresponding non-carbonate materials.

Crystal Structures of Betaine Phosphate/Arsenate Mixed Crystal

Single crystals of a betaine-phosphate/arsenate mixed system (30% P was replaced with As randomly) were investigated by means of X-ray diffraction. The crystal structures of room temperature and of low temperature (20 K) were determined. At room temperature, the least-squares calculation converged at the R factor 3.6% with 1038 reflections. The structure is isomorphous to pure betaine phosphate. For the low-temperature structure the R factor converged at 4.3% with 4896 reflections (3.7% with 2987 normal reflections and 9.6% with 1909 superlattice reflections). The structure analysis clarifies that the hydrogen atoms of the phosphoric acid between neighboring phosphate tetrahedra are ordered in the low temperature phase resulting the superstructure (the unit cell dimension along the a -axis is doubled). By replacing P with As up to 30% in P(As)O 4 tetrahedra, the unit cell structure is changed little; only the mean size of the tetrahedra is enlarged by 2.2%.

Structural and vibrational behaviour of fluorapatite with pressure. Part II: in situ micro-Raman spectroscopic investigation

High-pressure Raman investigations were carried out on a synthetic fluorapatite up to about 7 GPa to analyse the behaviour of the phosphate group's internal modes and of its lattice modes. The Raman frequencies of all modes increased with pressure and a trend toward reduced splitting was observed for the PO4-stretching modes [(ν3a(Ag) and ν3b(Ag); ν3a(E2g) and ν3b(E2g)] and the PO4 out-of-plane bending modes [ν4a(Ag) and ν4b(Ag)]. The pressure coefficients of phosphate modes ranged from 0.0047 to 0.0052 GPa−1 for ν3, from 0.0025 to 0.0044 GPa−1 for ν4, from 0.0056 to 0.0086 GPa−1 for ν2 and 0.0046 for ν1 GPa−1, while the pressure coefficients of lattice modes ranged from 0.0106 to 0.0278 GPa−1. The corresponding Gruneisen parameters varied from 0.437 to 0.474, 0.428, 0.232 to 0.409 and 0.521 to 0.800 for phosphate modes ν3, ν1, ν4, ν2, respectively, and from 0.99 to 2.59 for lattice modes. The vibrational behaviour was interpreted in view of the high-pressure structural refinement performed on the same crystal under the same experimental conditions. The reduced splitting may thus be linked to the reduced distortion of the environment around the phosphate tetrahedron rather than to the decrease of the tetrahedral distortion itself. Moreover, the amount of calcium polyhedral compression, which is about three times the compression of phosphate tetrahedra, may explain the different Gruneisen parameters.

Structural and vibrational behaviour of fluorapatite with pressure. Part I: in situ single-crystal X-ray diffraction investigation

Using single-crystal X-ray diffraction from a diamond anvil cell, the compressibility of a synthetic fluorapatite was determined up to about 7 GPa. The compression pattern was anisotropic, with greater change along a than c. Unit cell parameters varied linearly with β a =3.32(8) 10−3 and β c =2.40(5) 10−3 GPa−1, giving a ratio β a :β c =1.38:1. Data fitted with a third-order Birch-Murnaghan EOS yielded a bulk modulus of K 0=93(4) GPa with K′=5.8(1.8). The evolution of the crystal structure of fluorapatite was analysed using data collected at room pressure, at 3.04 and 4.72 GPa. The bulk modulus of phosphate tetrahedron is about three times greater than the bulk modulus of calcium polyhedra. The values were 270(10), 100(4) and 86(3) GPa for P, Ca1 (nine-coordinated) and Ca2 (seven-coordinated) respectively. While the calcium polyhedra became more regular with pressure, the distortion of the phosphate tetrahedron remained unchanged. The size of the channel extending along the [001] direction represented the most compressible direction. The Ca2–Ca2 distance decreased from 3.982 to 3.897 A on compression from 0.0001 to 4.72 GPa. The anisotropic compressional pattern may be understood in terms of the greater compressibility of the channel size over the polyhedral units. The reduction of the channel volume was measured by the evolution of the trigonal prism, having the Ca2–Ca2–Ca2 triangle as its base and the c lattice parameter as its height. This prism volume changed from 47.3 A3 at room pressure to 44.78 A3 at 4.72 GPa. Its relatively high bulk moduli, 86(3) GPa, indicated that the channel did not collapse with pressure and the apatite structure could remain stable at very high pressure.

Co(en)3][B(2)P(3)O(11)(OH)(2)]: a novel borophosphate templated by a transition-metal complex.

The structure of the title compound is made of chains of corner-sharing phosphate and borate tetrahedra that are separated by stacks of the octahedral Co(III) complex with ethylenediamine.

NaZn(H2O)2[BP2O8].H2O: a novel open-framework borophosphate and its reversible dehydration to microporous sodium zincoborophosphate N.

Crystals of NaZn(H2O)2[BP2O8].H2O were grown under mild hydrothermal conditions at 170 degrees C. The crystal structure (solved by X-ray single-crystal methods: hexagonal, P6(1)22 (no. 178), a = 946.2(2), c= 1583.5(1) pm, V= 1227.8(4).10(6) pm3, Z = 6) exhibits a chiral octahedral-tetrahedral framework related to the CZP topology and contains helical ribbons of corner-linked borate and phosphate tetrahedra. Investigation of the thermal behavior up to 180 degrees C shows a (reversible) dehydration process; this leads to the microporous compound Na[ZnBP2O8].H2O, which has the CZP topology. The crystal structure of Na[ZnBP2O8].H2O was determined by X-ray powder diffraction by using a combination of simulated annealing, lattice-energy minimization, and Rietveld refinement procedures (hexagonal, P6(1)22 (no. 178), a = 954.04(2), c = 1477.80(3) pm, V= 164.88(5).10(6) pm3, Z = 6). The essential structural difference caused by the dehydration concerns the coordination of Zn2- changing from octahedral to tetrahedral arrangement.

Vibrational spectroscopic study of dl-methionine dihydrogen phosphate

The two methionine cations in the asymmetric part of the unit cell of bis( dl-methionine dihydrogen phosphate) have different conformations. This, together with the different environments seen by the two CH 2 groups in each skeleton cause several of the group wavenumbers to occur as doublets or as broad bands. The anion contains two dissimilar PO bonds, which distorts the phosphate tetrahedron. Due to this, the stretching wavenumbers appear as doublets. There is extensive hydrogen bonding in the system in all three crystallographic directions and this is responsible for the changes in the position and intensity of several bands. Fermi resonance has also been observed.