Final Agreement Factors Research Articles

Neutron diffraction study of [H(4)Co(4)(C(5)Me(4)Et)(4)], a tetrahedral metal cluster complex with four face-bridging hydride ligands.

A single-crystal neutron diffraction analysis of the cluster complex [H(4)Co(4)(C(5)Me(4)Et)(4)] was carried out on the new quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin. The structure consists of four face-bridging hydrides attached to a tetrahedral cobalt metal core. Average distances and angles in the core of the molecule are as follows: Co-Co = 2.571(8), Co-C = 2.158(6), Co-H = 1.749(7), H.H = 2.366(9) A; Co-H-Co = 94.6(3), H-Co-H = 85.1(3) degrees. The hydride ligands are located off the Co-Co-Co planes by an average distance of 0.923(8) A. It is suggested that the dimensions of the HCo(3) fragments found in this molecule provide reasonable estimates for analogous distances and angles associated with chemisorbed H atoms situated on the 3-fold hollows of a cobalt surface. Crystallographic details: space group P2(1)/a (monoclinic); a = 21.979(2), b = 10.924(1), c = 34.406(2) A; beta = 90.81(1) degrees; Z = 8. Final agreement factor: R(F) = 0.099 for 3779 reflections [I > 2sigma(I)] collected at 20 K.

First Structural Analysis of a Naphthalene-Based Poly(ether ketone): Crystal and Molecular Simulation from X-ray Powder Data and Diffraction Modeling

Polycondensation of 2,6-dihydroxynaphthalene with 4,4‘-bis(4‘ ‘-fluorobenzoyl)biphenyl affords a novel, semicrystalline poly(ether ketone) with a melting point of 406 °C and glass transition temperature (onset) of 168 °C. Molecular modeling and diffraction-simulation studies of this polymer, coupled with data from the single-crystal structure of an oligomer model, have enabled the crystal and molecular structure of the polymer to be determined from X-ray powder data. This structurethe first for any naphthalene-containing poly(ether ketone)is fully ordered, in monoclinic space group P21/b, with two chains per unit cell. Rietveld refinement against the experimental powder data gave a final agreement factor (Rwp) of 6.7%.

Neutron diffraction study of the highly distorted octahedral complex FeH 2(CO) 2[P(OPh) 3] 2

A neutron diffraction analysis was carried out at 20 K on a single crystal of FeH 2(CO) 2[P(OPh) 3] 2 in order to accurately locate the hydride ligands. The two hydrides are bonded terminally to the Fe atom, and their small size causes the title complex to assume a highly distorted octahedral geometry. Distances and angles involving the hydride ligands are as follows: FeH(1)=1.521(2) Å, FeH(2)=1.529(2) Å, H(1)⋯H(2)=2.011(3) Å, and H(1)FeH(2)=82.49(13)°. Final agreement factors: R( F)=2.8% and R( wF 2)=5.4%.

Critical Role of Diffraction Simulation in Establishing the Crystal and Molecular Structures of Poly(biaryl ether ketone)s

Molecular modeling and diffraction simulation studies of the biphenyl-based poly(ether ketone)s [O−Ar−Ar−O−Ar−CO−Ar−Ar−CO−Ar−]n (3) and [−O−Ar−Ar−CO−Ar−]n (4, Ar = 1,4-phenylene), coupled with data obtained from an oligomer single-crystal study, have enabled their crystal and molecular structures to be determined from X-ray powder data. A crystallographically disordered structure in which the ether and ketone linkages are distributed randomly over the bridging positions of the polymer chain is potentially available to both polymers and undoubtedly occurs in their random 1:2 copolymer (5). The disordered structure is monoclinic (rather than orthorhombic as has previously been proposed), in space group P21/b, with two chains per unit cell. Rietveld refinement of this structure for polymers 3 and 4, based on X-ray powder data, gave final agreement factors (Rwp) of 5.7% and 6.6%, respectively. Analysis of X-ray fiber data by diffraction simulation methods suggests that the disordered structure always predomin...

Hydrogen bond network of the layered phosphates γ-Zr(H2PO4)(PO4)⋅2H2O and γ-Hf(H2PO4)(PO4)⋅2H2O determined by neutron powder diffraction

Abstract The hydrogen atom positions of the layered phosphates Zr(PO4)(H2PO4)⋅2H2O (γ-ZrP) and Hf(PO4)(H2PO4)⋅2H2O (γ-HfP) have been determined from neutron powder diffraction data and the complete crystal structures have been refined by the Rietveld method. The compounds crystallize in the monoclinic space group P21. The final agreement factors are: R wp = 1.47, R exp = 0.91 for γ-ZrP and R wp = 1.73, R exp = 1.43 for γ-HfP. The two compounds are isostructural and posses a dense hydrogen-bonding network. They are formed by layers consisting of two planes of metallic atoms joined by phosphate and dihydrogenphosphate groups. The interlayer space form channels where each water molecule accepts and donates an hydrogen bond to another water molecule forming a zig-zag chain. Additionally each water molecule acts as acceptor and donor in two hydrogen bonds with oxygen atoms of the same layer. Consecutive layers are, in this way, indirectly held together by hydrogen bonds through the water molecules.

Synthesis and characterisation of MIL-43 and MIL-44, two new layered templated tetravalent phosphates: Zr(PO4)2·N2C2H10 and Ti2(PO4)2(HPO4)2·N2C2H10

Zr(PO4)2·N2C2H10 or MIL-43 and Ti2(PO4)2(HPO4)2·N2C2H10 or MIL-44 were prepared hydrothermally (20 or 4 days, 473 or 453 K, respectively, autogenous pressure) in the presence of ethylenediamine. Their structures have been determined by single-crystal X-ray diffraction. MIL-43 crystallises in the monoclinic space group P21 (No. 4) with a=11.0722(1), b=10.6631(1), c=16.4642(2) Å, β=95.991(1)° and V=1933.21(3) Å3 (final agreement factors R1(F)=0.0466, wR2(F2)=0.1096). Due to the very poor quality of the crystal, only an approached structure of MIL-44 is given; it crystallises in the triclinic space group P1 (No. 1) with a=5.0845(4), b=6.3097(5), c=12.6111(9) Å, α=77.454(1), β=78.926(2), γ=89.986(1)° and V=387.21(5) Å3. Both solids are two-dimensional and are the ion-exchanged equivalents of the layered solids αZrP and γTiP. Inorganic sheets of MIL-43 are built up from pseudo-hexagonal arrays of ZrO6 octahedra surrounded by PO4 tetrahedra pointing their terminal oxygen alternatively up and down at the interlayer space. Layers of MIL-44 are made of double (TiOP) chains built from TiO6 octahedra and PO4 tetrahedra on which HPO4 groups are grafted pointing towards the interlayer space. In both cases, diprotonated organic templates, located between the layers, interact with terminal phosphate groups and ensure via hydrogen bonds the stability of the structures.

SYNTHESIS AND CHARACTERIZATION OF A LINEAR μ-OXO DIIRON(III) COMPOUND AND A COPPER(II) NITRITE COMPLEX CONTAINING, A TRIPODAL POLYBENZIMIDAZOLE LIGAND

Iron(III) and copper(II) complexes of the polybenzimidazole ligand, tris((benzimidazol-2-yl)methyl)amine (tmba) have been synthesized and structurally characterized. The mononuclear complex [Cu(tmba)(NO2)]+[CH3OH][NO− 2], 1, has been isolated and characterized by X-ray crystallography. The complex crystallizes in the triclinic space group P1 with two molecules in the unit cell of dimension a = 8.891(5), b = 11.775(6), and c = 13.702(8)Å, and α = 67.76(1), β = 71.79(2) and γ = 88.96(1)°, and volume = 1253.0(12)Å3. The structure was refined to a final agreement factor R = 0.0901 using 4134 observed reflections. The complex consists of cationic copper(tmba) complex covalently bonded to a nitrite, and a pair of these cations is dibridged by a pair of nitrite anions. The gap between this dimer is occupied by a methanol molecule. The coordination environment around each copper can be described as trigonal bipyramidal, with the tertiary amine, a benzimidazole nitrogen and an oxygen from the nitrite providing the ligating atoms of the trigonal plane. The μ-oxo bridged binuclear complex [Fe2O(tmba)2Cl2](H2O)(EtOH)2·Cl2, 2, was also characterized by single crystal X-ray diffraction and magnetic susceptibility. The complex crystallizes in the triclinic space group P1 with one molecule in the unit cell of dimensions, a = 11.5791(7), b = 13.3369(8), and c = 13.7002(9) Å, and α = 103.904(1), β = 108.903(2) and γ = 112.845(1)°, and volume = 1674.1(2) å3. The structure was refined to a final agreement factor R = 0.073 using 5597 observed reflections. The complex is a centrosymmetric dimer, with the two iron(III) atoms bridged by an oxygen atom, with an Fe—O—Fe angle of 180°, and a Fe—Fe distance of 3.61(1)Å. The coordination around each iron(III) is best described as octahedral, with the bridging oxygen trans to one end of the benzimidazole group, and a chlorine atom trans to the tertiary amine nitrogen of the ligand.

Localization of potassium in substituted lead hydroxyapatite: Pb9.30K0.60(PO4)6(OH)1.20 by X-ray diffraction

An adaptation of the double decomposition method for apatites preparation is tested on lead apatite and applied to the synthesis of lead hydroxyapatite partially potassium substituted. The structure of the sample is carried out by the Rietveld method using powder XRD measurement. The compound crystallizes in the hexagonal system (space group P 6 3 / m ) with the following cell: a = b =9.8461(3) Å, c =7.3591(3) Å. Final agreement factors R p , R wp , R B , and R F are 0.16, 0.11, 0.037, and 0.031, respectively. Results are discussed and compared with those for Pb 10 (PO 4 ) 6 (OH) 2 . According to site occupancy factors, potassium prefers to occupy the site 4f (site(I)). Moreover the structure contains vacancies in both lead and hydroxyl sites. A global mechanism of potassium substitution for lead is proposed.

Crystallization and Structural Characteristics of New Borosilicates

Crystals of stillwellite-like lanthanum borosilicate were obtained from high-temperature solutions. Lithium and potassium di- and trimolybdates were used as fluxes for silicate systems. In the case of borosilicate crystals, the choice of fluxes was based on the potassium trimolybdate with an excess of potassium fluoride. The composition of grown crystals was studied by electron microprobe analysis, and structural characteristics were determined for the La3BSi2O10. It crystallizes in the orthorhombic system, space group Pbca, with cell dimensions a=9.977(2), b=7.269(2), c=23.410(2) Å, V=1697.8(6) Å3, and final agreement factors R=0.059, Rw=0.089.

REFINEMENT OF THE STRUCTURE OF BANDYLITE

The structure of bandylite, Cu 2[B(OH)4]2Cl2, Z = 1, tetragonal, a 6.171(2), c 5.587(3) A, V 212.7 A 3 , space group P4/n, has been refined by full-matrix least-squares techniques on the basis of F 2 using 263 unique reflections collected with Mo Ka X-radiation and a CCD (charge-coupled device) area detector. The final agreement factor ( R1) was 3.7% and the goodness-of-fit (S) was 0.90 for the 144 unique observed reflections (|F o| > 4sF). The structure consists of mixed-ligand Jahn‐Teller-distorted Cu(OH)4Cl2 octahedra and B(OH)4 tetrahedra that are linked by vertex sharing.

Trimerization of NaC2N3 to Na3C6N9 in the Solid: Ab Initio Crystal Structure Determination of Two Polymorphs of NaC2N3 and of Na3C6N9 from X-ray Powder Diffractometry

Sodium dicyanamide NaC2N3 was found to undergo two phase transitions. According to thermal analysis and temperature-dependent X-ray powder diffractometry, the transition of alpha-NaC2N3 (1a) to beta-NaC2N3 (1b) occurs at 33 degrees C and is displacive. 1a crystallizes in the monoclinic system, space group P21/n (no. 14), with a = 647.7(1), b = 1494.8(3), c = 357.25(7) pm, beta = 93.496(1) degrees, and Z = 4. The structure was solved from powder diffraction data (Cu Kalpha1, T = 22 degrees C) using direct methods and it was refined by the Rietveld method. The final agreement factors were wRp = 0.072, Rp = 0.053, and RF = 0.074. 1b crystallizes in the orthorhombic system, space group Pbnm (no. 62), with a = 650.15(5), b = 1495.1(2), c = 360.50(3) pm, and Z = 4. The structure was refined by the Rietveld method using the atomic coordinates of 1a as starting values (Mo Kalpha1, T = 150 degrees C). The final agreement factors were wRp = 0.044, Rp = 0.034, RF = 0.140. The crystal structures of both polymorphs contain sheets of Na+ and N(CN)2- ions which are in la nearly and in 1b exactly coplanar. Above 340 degrees C, 1b trimerizes in the solid to Na3C6N9 (2). 2 crystallizes in the monoclinic system, space group P21/n (no. 14), with a = 1104.82(1), b = 2338.06(3), c = 351.616(3) pm, beta = 97.9132(9)degrees, and Z = 4. The structure was solved from synchrotron powder diffraction data (lambda = 59.733 pm) using direct methods and it was refined by the Rietveld method. The final agreement factors were wRp = 0.080, Rp = 0.059, and RF = 0.080. The compound contains Na+ and the planar tricyanomelaminate C6N9(3-). The phase transition from 1b to 2 is reconstructive. It occurs in the solid-state without involvement of other phases or intermediates. The crystal structures of 1b and 2 indicate that there is no preorientation of the N(CN)2- in the solid before their trimerization to C6N9(3-).

Trimerization of NaC2N3 to Na3C6N9 in the Solid

Sodium dicyanamide NaC2N3 was found to undergo two phase transitions. According to thermal analysis and temperature-dependent X-ray powder diffractometry, the transition of α-NaC2N3 (1a) to β-NaC2N3 (1b) occurs at 33°C and is displacive. 1a crystallizes in the monoclinic system, space group P21/n (no. 14), with a = 647.7(1), b = 1494.8(3), c = 357.25(7) pm, β = 93.496(1)°, and Z = 4. The structure was solved from powder diffraction data (Cu Kα1, T = 22°C) using direct methods and it was refined by the Rietveld method. The final agreement factors were wRp = 0.072, Rp = 0.053, and RF = 0.074. 1b crystallizes in the orthorhombic system, space group Pbnm (no. 62), with a = 650.15(5), b = 1495.1(2), c = 360.50(3) pm, and Z = 4. The structure was refined by the Rietveld method using the atomic coordinates of 1a as starting values (Mo Kα1, T = 150°C). The final agreement factors were wRp = 0.044, Rp = 0.034, RF = 0.140. The crystal structures of both polymorphs contain sheets of Na+ and N(CN)2- ions which are in 1a nearly and in 1b exactly coplanar. Above 340°C, 1b trimerizes in the solid to Na3C6N9 (2). 2 crystallizes in the monoclinic system, space group P21/n (no. 14), with a = 1104.82(1), b = 2338.06(3), c = 351.616(3) pm, β = 97.9132(9)°, and Z = 4. The structure was solved from synchrotron powder diffraction data (λ = 59.733 pm) using direct methods and it was refined by the Rietveld method. The final agreement factors were wRp = 0.080, Rp = 0.059, and RF = 0.080. The compound contains Na+ and the planar tricyanomelaminate C6N93-. The phase transition from 1b to 2 is reconstructive. It occurs in the solid-state without involvement of other phases or intermediates. The crystal structures of 1b and 2 indicate that there is no preorientation of the N(CN)2- in the solid before their trimerization to C6N93-.

Hybrid open frameworks (MIL- n): synthesis and crystal structure of MIL-17 — a rare-earth dicarboxylate with a relatively open framework, [Pr(H 2O)] 2[O 2C(CH 2) 2CO 2] 3·H 2O

A new rare-earth dicarboxylate [Pr(H 2O)] 2[O 2C(CH 2) 2CO 2] 3·H 2O (MIL-17) was hydrothermally prepared (180°C, 3 days) by reaction of succinic acid with the metal chloride in the ratio 1:1. The crystal structure of the compound has been determined by single-crystal X-ray diffraction. [Pr(H 2O)] 2[O 2C(CH 2) 2CO 2] 3·H 2O crystallizes in the monoclinic space group C2/c (No. 15) with a=20.2586(8) Å, b=7.9489(3) Å, c=13.9716(5) Å, β=121.641(1)° (final agreement factors R 1=0.0282, wR 2=0.0764). The organic–inorganic network is three-dimensional and consists of edge-sharing rare-earth polyhedra LnO 8(H 2O) chains linked together by the carbon chains along two directions as already encountered in [Pr(H 2O)] 2[O 2C(CH 2) 3CO 2] 3·4H 2O. The connection in [Pr(H 2O)] 2[O 2C(CH 2) 2CO 2] 3·H 2O involves the formation of tunnels large enough to incorporate one weakly bonded water molecule.

Hybrid Organic-Inorganic Frameworks (MIL-n). Hydrothermal Synthesis of a Series of Pillared Lanthanide Carboxyethylphosphonates and X-ray Powder ab Initio Structure Determination of MIL-19, Pr[O(3)P(CH(2))(2)CO(2)

A series of lanthanide and yttrium carboxyethylphosphonates has been hydrothermally prepared (200 degrees C, 4 days) from the 1:1 mixture of carboxyethylphosphonic acid and the metal chlorides. The crystal structure of the praesodymium compound Pr(III)[O(3)P(CH(2))(2)CO(2)] has been determined ab initio from X-ray powder diffraction data and refined by the Rietveld method. The compound crystallizes in the monoclinic space group P2(1)/m (No. 11) with cell parameters at 20 degrees C a = 8.3617(2) Å, b = 7.1899(2) Å, c = 5.4586(2) Å, beta = 103.784(2) degrees, and Z = 2. The final agreement factors converged to the values R(p) = 0.139, R(wp) = 0.177, Bragg R = 0.123, R(F) = 0.055, and chi(2) = 3.50. The hybrid framework consists of inorganic Pr/O/P/C layers connected by organic groups, with an interlayer spacing of approximately 8.36 Å. The praesodymium atoms are 7-fold coordinated in this pillared layered structure. Isostructural compounds were prepared for yttrium and the entire series of the lanthanide elements.

A new self-assembled copper(I) complex of 2-thioxo-5H-1,3-dithiolo[4,5-b][1,4]dithiepin-6(7H)-one showing three-dimensional supramolecular networks

The synthesis and structural characterization of a supramolecular copper(I) complex of 2-thioxo-1,3-dithiolo[4,5-b][1,4]dithiepin-6(7H)-one are described. The complex crystallized in the orthorhombic space group Pna21 with the cell dimensions a=12.9124(2), b=20.7944(2), c=4.4457(1) Å, V=1193.70(3) Å3 and Z=4. The structure was refined to a final agreement factor R=0.0295. The C6H4OS5Cu units are connected by bridging iodide atoms to form a ladder structure. The Cu⋯Cu separation is 2.9884(9) Å, and the short S⋯S and S⋯I contacts interchain lead to a novel three-dimensional network.

Studies on Tetragonal Na2CoP2O7, a Novel Ionic Conductor

Crystals of the tetragonal form of Na2CoP2O7 have been grown and characterized by single crystal X-ray diffraction. This compound crystallizes in the tetragonal system, space group P42/mnm with a=7.7058(12), c=10.301(2) Å, and Z=4. The structure was solved by Patterson and Fourier methods, and refined to final agreement factors R(F2)=5.8%, Rw(F2)=12.4%, S(F2)=1.07. Their structure can be described as layered since it is formed by slabs of [CoP2O7]∞ with Na cations lying between the layers. The Co2+ cation adopts a tetrahedral coordination geometry unusual in inorganic solids. CoO4 tetrahedra share four oxygens with P2O7 pyrophosphate groups and the Na+ cations appear in a NaO8 quadrangular prismatic coordination geometry. Magnetic measurements reveal the presence of antiferromagnetic interactions in the Co2+ sublattice, at about 10 K. Magnetic correlations are also studied from the analysis of possible superexchange pathways in the structure. Impedance measurements (frequency range: 1–5×106 Hz; temperature range: 90–540°C) show Na2CoP2O7 an ionic conductor being the conductivity at 300°C 2×10−5 Scm−1 and the activation energy 0.61 eV. The possible motion of the Na+ ions in the interlayer surface plane and through adjacent layers (c axis) is discussed.

Hydrothermal synthesis and crystal structure of a new three-dimensional titanium(IV) phosphate with an open structure: Ti6O3(H2O)3(PO4)7•(H3O)3•H2O or MIL-18

Ti 6 O 3 (H 2 O) 3 (PO 4 ) 7 •(H 3 O) 3 •H 2 O or MIL-18 was prepared hydrothermally (3 days, 483 K, autogenous pressure) in the presence of an organic base (1–3 diaminopropane). Its structure has been determined by single-crystal X-ray diffraction. This compound crystallises in the hexagonal space group P 6 3 / m (no. 176) with a = 15.9562 (1) A, c = 6.2990 (1) A and V = 1388.9 (1) A 3 (final agreement factors R 1 ( F ) = 0.0391, wR 2 ( F 2 ) = 0.0779). Its three-dimensional framework is built up from the linkage of corner sharing TiO 6 and TiO 5 (H 2 O) octahedra with tetrahedral PO 4 groups. The structure presents -(Ti-O-P)- chains, related together via titanium dimers and phosphate groups, that delimit five-membered rings and corrugated twelve-membered ring channels, along the [001] direction, in which water molecules are interacting with terminal groups. Ti 6 O 3 (H 2 O) 3 (PO 4 ) 7 •(H 3 O) 3 •H 2 O OU MIL-18. Les phosphates de titane ont fait l'objet d'une attention toute particulière lors des précédentes décennies du fait de leur propriétés intéressantes (échange d'ion, conductivité ionique…). Toutefois, si la caractérisation structurale des phases denses obtenues par voie solide a été menée à son terme [1–10], très peu de composés avaient pu être obtenus par voie hydrothermale jusqu'à présent, si l'on excepte de rares composés tels que les phases αTiP et γTiP [11, 12]. Cependant, avec les progrès rencontrés dans le domaine de la détermination structurale à partir des données sur poudre, un certain nombre de phases nouvelles, lamellaires ou tridimensionnelles à charpente ouverte, ont été récemment caractérisées [13–16]. Par ailleurs, notre groupe a développé depuis 1992 une nouvelle série de metallophosphates (M = Al, Ga, Fe, V) oxyfluorés et structurés par des agents organiques, appelés ULM-n, [17–26]. Toutefois, peu de résultats ont concerné jusqu'à présent les éléments tétravalents si l'on excepte quelques fluorophosphates de zirconium caractérisés récemment [27–30]. Nous avons donc entrepris une étude systématique des systèmes correspondants avec le titane. Cela a permis la caractérisation des premiers fluorophosphates de titane(IV) (MIL-6) de formule Ti 2 (PO 4 ) 2 F 4 .N 2 C 2 Hi 10 et Ti 2 (PO 4 ) 2 F 4• N 2 C 3 H 12• H 2 O [31], ainsi que d'un nouveau fluorophosphate de titane à valence mixte, tridimensionnel à charpente ouverte: Ti Ti F(PO 4 ) 2• 2H 2 O (MIL-15) [32]. Cette note relate la synthèse et la détermination structurale d'un nouveau phosphate de titane(lV) à charpente ouverte: Ti 6 O 3 (H 2 O) 3 (PO 4 ) 7• (H 3 O) 3• H 2 O ou MIL-18. Ce composé n'a pu être obtenu que minoritairement sous forme de cristaux isolés et aucune analyse quantitative n'a pu ainsi être effectuée sur ce composé jusqu'à présent. Les calculs de lien de valence et l'analyse EDX ont montré l'absence de fluor et d'ammonium au sein de cette structure. Celle-ci est constituée à partir d'un assemblage d'octaèdres TiO 6 et TiO 5 (H 2 O) et de groupements tétraédriques PO 4 . Cela conduit à la formation de chaînes -(Ti-O-P)-, dirigées selon l'axe c , et qui sont connectées entre elles par l'intermédiaire des dimères d'octaèdres de titane et de connections de type Ti-O-P. Cela assure la tridimensionnalité de la structure et conduit à la formation de deux types de tunneis. Les premiers sont constitués à partir de cycles « gaufrésà 12 polyèdres comportant de l'eau non protonée en leur sein, et qui interagit avec de l'eau en position terminale liée aux atonies de titane appartenant aux cycles. Les seconds tunnels sont réalisés à partir de cycles à cinq polyèdres, connectés trois à trois par l'intermédiaire de groupements PO 4 ; de l'eau protonée est contenue dans ces tunnels et interagit fortement avec le réseau inorganique voisin. Des études sont en cours actuellement afin d'isoler cette phase en grande quantité, de manière à étudier ses propriétés d'insertion et son comportement thermique. En effet, si la déshydratation (totale) de MIL-18 ne conduit pas à la déstabilisation de sa structure, ce que laisse supposer l'étude du comportement thermique d'autre phosphates de titane tridimensionnels à charpente ouverte caractérisés auparavant [32, 33], celui-ci serait le premier phosphate de titane(IV) microporeux caractérisé jusqu'ici. © Académie des sciences/Elsevier, Paris

Determination of Formation Regions of Titanium Phosphates; Determination of the Crystal Structure ofβ-Titanium Phosphate, Ti(PO4)(H2PO4), from Neutron Powder Data

The formation region of the various types of layered titanium hydrogen phosphate hydrates was investigated. The materials were prepared by hydrothermal methods, treating amorphous titanium phosphate with phosphoric acid (8 to 16M) in the temperature range 175 to 250°C. The materials obtained were:α-Ti(HPO4)2·H2O,γ-Ti(PO4)(H2PO4)·2H2O, and its anhydrous formβ-Ti(PO4)(H2PO4). The structure ofβ-Ti(PO4)(H2PO4) has been determined by Rietveld powder refinement of high resolution neutron diffraction data. The structure is refined in the monoclinic space groupP21/n(No. 14). The unit cell parameters are:a=18.9503(4) Å,b=6.3127(1) Å,c=5.1391(1) Å,β=105.366(2)°;Z=4. The final agreement factors were:Rp=2.9% andRwp=3.8%. The structure ofβ-Ti(PO4)(H2PO4) is built from TiO6octahedra linked together by tertiary phosphate (PO4) and dihydrogen phosphate ((OH)2PO2) tetrahedra. The layers are held together by hydrogen bonds.

Aluminum Phenylphosphonates: A Fertile Family of Compounds.

Six aluminum phenylphosphonates have been synthesized depending upon the synthetic conditions: Al(2)(O(3)PC(6)H(5))(3).2H(2)O (I), Al(2)(O(3)PC(6)H(5))(3) (II), alpha-Al(HO(3)PC(6)H(5))(O(3)PC(6)H(5)).H(2)O (III), beta-Al(HO(3)PC(6)H(5))(O(3)PC(6)H(5)).H(2)O (IV), Al(HO(3)PC(6)H(5))(3).H(2)O (V), and Al(OH)(O(3)PC(6)H(5)) (VI). Thermal analysis, X-ray powder thermodiffractometry, IR spectroscopy, and (27)Al and (31)P MAS NMR data have been obtained to study the structure and thermal stability of these materials. III crystallizes in the orthorhombic system, space group Pbca, with a = 9.7952(1) Å, b = 29.3878(4) Å, c = 9.3537(3) Å, and Z = 8. The structure was solved ab initio, from synchrotron data (lambda approximately 0.4 Å), using direct methods, and refined by Rietveld methods. The final agreement factors were R(wP) = 6.73%, R(P) = 5.24%, and R(F)() = 6.8%. The compound is layered with the aluminum atoms in an octahedral environment of oxygens and two crystallographically independent phosphonate groups, one being protonated. The powder patterns of V and VI have been indexed, and the experimental observations are consistent with layered structures. The unit cell of V contains one octahedral site for Al and three tetrahedral sites for P. Phosphonate I seems to have a three-dimensional tubular structure with aluminum atoms in both octahedral and tetrahedral environments and phosphorus atoms in three different types of sites.

Synthesis, ab initio structure determination, and characterization of manganese(III) phenyl phosphonates

Two new manganese(III) phenyl phosphonates, Mn(HO 3PC 6H 5)(O 3PC 6H 5)·H 2O and Mn(HO 3PC 6H 5)(O 3PC 6H 5), were synthesized. The crystal structure of Mn(HO 3PC 6H 5)(O 3PC 6H 5) was solved ab initio from powder X-ray diffraction data. This compound crystallizes in the triclinic system, a = 10.2149(5), b = 15.0028(8), c = 5.0324(3) Å, α = 95.563(4)°, β = 116.858(4)°, γ = 95.684(5)°, V = 675.87(6) Å 3, space group P 1 , and Z = 2. The final agreement factors were R WP = 12.8%, R P = 9.1%, and R F = 3.2%. There are 22 non-hydrogen atoms in the asymmetric part of the unit cell, and the positional parameters were refined with the help of soft constraints. The octahedral manganese coordination spheres are distorted due to the Jahn-Teller effect. The structure of this organic–inorganic compound is layered. The thermal behavior of Mn(HO 3PC 6H 5)(O 3PC 6H 5)·H 2O was studied and its thermal decomposition product was identified.