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A better understanding of the effects of temperature and pressure on the wide gap SiC semiconductor is necessary for both (i) an improvement of the performance of this compound in a variety of technological applications and (ii) a clarification of controversial issues related to the stability of its cubic polymorphs at high pressure and high temperature. Bearing in mind this double demand, we perform first-principles calculations of the phonon band structures, vibrational density of states, and thermal and mode Grüneisen parameters of the zinc blende (B3) and rock-salt (B1) cubic polymorphs of 3C-SiC covering pressures and temperatures up to 120 GPa and 3000 K, respectively. Under a martensitic description of the B3-B1 transformation, we found that the large hysteresis pressure range observed at room temperature (35-100 GPa) disappears at around 1100 K. The calculated Clapeyron slope of this transformation is slightly negative, with average values of -2.9 MPa K

A two-step transition path for alkaline earth carbonates via a hexagonal structure is able to clarify previous controversial results and provide useful information on the Earth's C-cycle.

To advance in the understanding of the Earth's carbon cycle, it is necessary to determine thermodynamic boundaries and kinetic barriers associated with the pressure-induced polymorphic sequence of alkaline-earth carbonates. Following a symmetry-based strategy within the martensitic approximation, we propose a two-step mechanism mediated by a hexagonal

The crystal structure of many inorganic compounds can be understood as a metallic matrix playing the role of a host lattice in which the nonmetallic atomic constituents are located, the Anions in Metallic Matrices (AMM) model stated. The power and utility of this model lie in its capacity to anticipate the actual positions of the guest atoms in inorganic crystals using only the information known from the metal lattice structure. As a pertinent test-bed for the AMM model, we choose a set of common metallic phases along with other nonconventional or more complex structures (face-centered cubic (fcc) and simple cubic Ca, CsCl-type BaSn, hP4-K, and fcc-Na) and perform density functional theory electronic structure calculations. Our topological analysis of the chemical pressure (CP) scalar field, easily derived from these standard first-principles electronic computations, reveals that CP minima appear just at the precise positions of the nonmetallic elements in typical inorganic crystals presenting the above metallic subarrays: CaF

A thorough investigation of pressure effects on the structural properties of crystalline cesium uranyl chloride was performed by means of first-principles calculations within the density functional theory framework. Total energies, equilibrium geometries and vibrational frequencies were computed at selected pressures up to 50 GPa. Zero pressure results present good agreement with available experimental and theoretical data. Our calculated equation of state parameters reveal that Cs2UO2Cl4 is a high compressible material, similar to other ionic compounds with cesium cations, and displays a structural anisotropic behavior guided by the uranyl moiety. An unexpected variation of the U-O bond length, dUO, is detected as pressure is applied. It leads to a dUO-stretching frequency relationship that cannot be described by the traditional Badger's rule. Interestingly enough, it can be explained in terms of a change in the main factor controlling dUO. At low pressure, the charge transferred to the uranyl cation induces an increase of the bond length and a red shift of the stretching frequencies, whereas it is the mechanical effect of the applied pressure above 10 GPa that is the dominant factor that leads to a shortening of dUO and a blue shift of the stretching frequencies.

The characterization of bonding interactions in molecules and materials is one of the major applications of quantum mechanical calculations. Numerous schemes have been devised to identify and visualize chemical bonds, including the electron localization function, quantum theory of atoms in molecules, and natural bond orbital analysis, whereas the energetics of bond formation are generally analyzed in qualitative terms through various forms of energy partitioning schemes. In this Article, we illustrate how the chemical pressure (CP) approach recently developed for analyzing atomic size effects in solid state compounds provides a basis for merging these two approaches, in which bonds are revealed through the forces of attraction and repulsion acting between the atoms. Using a series of model systems that include simple molecules (H2, CO2, and S8), extended structures (graphene and diamond), and systems exhibiting intermolecular interactions (ice and graphite), as well as simple representatives of metallic a...

The determination of kinetic factors affecting phase metastability is crucial for the design of materials out of the ambient conditions. At a given temperature, the kinetic barrier associated with the reconstruction of the bonding network of a pressure-induced phase transition can be only overcome at pressures where the available vibrational energy of the system is equal or higher than the corresponding activation energy. Our work demonstrates that these pressures provide boundaries to hysteresis cycles that can be evaluated following a three-step computational strategy: (i) total energy electronic structure calculations, (ii) determination of vibrational contributions by means of a simple Debye model, and (iii) description of the energetic profile along the transition path in the framework of the martensitic approximation. In the 3C-SiC polytype, our results reveal that the high pressure rock-salt (B1) structure can not be quenched on release of pressure unless temperature is close to 0 K. The B1 phase transforms back to the low-pressure zinc blende (B3) polymorph at 300 K if pressure is below 30 GPa, in very good agreement with experimental observations. These results are supported by a full characterization of the B3-B1 energetic transition profile in terms of the chemical changes of the bonding network topologically analysed with the electron localization function.

The interplay of structural, energetic, and chemical bonding features across the pressure-induced α-cristobalite → stishovite phase transition in SiO2 is fully characterized by first principles calculations and topological analysis of the electron localization function. Under a martensitic approach, the transition mechanism is theoretically modeled at the thermodynamic transition pressure using the α-cristobalite P41212 space group. A soft and symmetric transition path is determined with an activation barrier lower than 100 kJ/mol. No bond breaking is found, but a synchronous bonding formation process leading to Si 6-fold and O 3-fold coordinations. Only when the third coordination sphere of oxygens approaches a given Si at a distance close to 2.0 A do new Si–O bonding basins appear. This situation occurs at a transformation stage well beyond the maximum in the energetic profile of the transition path.

The response of 3C-SiC to hydrostatic pressure and to several uni- and bi-axial stress conditions is thoroughly investigated using first principles calculations. A topological interpretation of the chemical bonding reveals that the so-called non-covalent interactions enhance only at high pressure while the nature of the covalent Si–C bonding network keeps essentially with the same pattern. The calculated low compressibility agrees well with experimental values and is in concordance with the high structural stability of this polymorph under hydrostatic pressure. Under uniaxial [001] stress, the c/a ratio shows a noticeable drop inducing a closure of the band gap and the emergence of a metallic state around 40 GPa. This behavior correlates with a plateau of the electron localization function exhibiting a roughly constant and non-negligible value surrounding CSi4 and SiC4 covalent bonded units.

Microcrystals of the first ammonium-thorium phosphates, (NH 4) 2Th(PO 4) 2.H 2O (tetragonal, I4 1/ amd, a = 7.0192(4) A, c = 17.9403(8) A) and NH 4Th 2(PO 4) 3 (monoclinic, C2/ c, a = 17.880(6) A, b = 6.906(1) A, c = 8.152(2) A, beta = 104.39(2) degrees ) were hydrothermally obtained from a Th(NO 3) 4-CO(NH 2) 2-H 3PO 3-H 2O system ( T = 180 degrees C). In both cases, the structure consists of a three-dimensional framework with PO 4 tetrahedra coordinated to Th atoms (ThO n polyhedra, where n = 8 or 9, for the tetragonal or monoclinic phase, respectively). The ammonium ions (and water molecules) are located in the tunnels.

Fe(H{sub 2}PO{sub 4})(H{sub 2}P{sub 2}O{sub 7}).C{sub 5}H{sub 5}N, a new iron(III) phosphate with an open-framework has been synthesized hydrothermally using pyridine as organic template. The crystal structure was solved ab initio using conventional powder X-ray diffraction data. The unit cell is orthorhombic, a=9.5075(2), b=10.1079(1), c=13.3195(2) A, space group P2{sub 1}2{sub 1}2{sub 1}, Z=4. The structure consists of FeO{sub 6} octahedra joined by H{sub 2}PO{sub 4} and H{sub 2}P{sub 2}O{sub 7} groups forming linear chains interconnected by hydrogen bonding to give rise to a supramolecular framework enclosing tunnels in which the pyridine molecules reside. - Graphical abstract: The low temperature hydrothermal synthesis offers many possibilities in the preparation of new materials with mixed octahedral-tetrahedral open-frameworks. Fe(H{sub 2}PO{sub 4})(H{sub 2}P{sub 2}O{sub 7}).C{sub 5}H{sub 5}N is constituted by linear chains of FeO{sub 6} octahedra joined through of both dihydrogenphosphate and dihydrogendiphosphate bridges, interconnected by hydrogen bonds, originating channels where the pyridine molecules are located.

Two new phosphate compounds, KNiPO4·6H2O and NaNiPO4·7H2O, have been synthesized, identified and their crystal structure studied by powder X-ray diffraction. KNiPO4·6H2O crystallizes in the monoclinic system, with lattice parameters a = 6.8309(3) A, b = 11.0610(4) A, c = 6.1165(2) A, and angle β = 91.045(2)°, volume of the unit cell V = 462.07(3) A3, space group P21, and Z = 2, while NaNiPO4·7H2O does so in the tetragonal system with a = 6.7390(2) A, c = 10.9690(4) A, V = 498.15(4) A3, space group P42/mmc, and Z = 2. KNiPO4·6H2O has the structure as the struvite analogue KMgPO4·6H2O, whereas NaNiPO4·7H2O is isostructural with the compound NaMgPO4·7H2O. Neither material presents a magnetic order in the range of temperatures measured from 300 K down to 1.8 K.

Th(2)(PO(4))(2)(HPO(4)).H(2)O was synthesized under wet hydrothermal conditions starting from a mixture of H(3)PO(3) and Th(NO(3))(4).5H(2)O. The crystal structure was solved by powder X-ray diffraction data. The unit cell parameters are a = 6.7023(8) Angstroms, b = 7.0150(8) Angstroms, c = 11.184(1) Angstroms, beta = 107.242(4) degrees, space group P2(1), and Z = 2. The structure consists of layers of both thorium atoms and PO(4) groups, alternating with a layer formed by HPO(4) entities and water molecules. By thermal treatment, this compound turns into Th(4)(PO(4))(4)P(2)O(7), a ceramic already described in the field of the immobilization of tetravalent actinides.

K 2 MSi 3 O 9 ·H 2 O (M = Sn, Pb) synthetic framework silicates are isotypical with umbite and kostylevite minerals, respectively. The silicate anion exhibits two structural types, one of which is an infinite chain polysilicate (umbite) and the other a cyclohexasilicate (kostylevite). The structural formulas may be written as K 2 Sn{ uB , 1 ∞ 1 }[ 3 Si 3 O 9 ]H 2 O and K 4 Pb 2 { uB , 1 r }[Si 6 O 18 ]2H 2 O. The thermal behavior of these compounds was determined by dynamic and isothermal thermogravimetry combined with powder X-ray diffraction between room temperature and 550 °C. The kostylevite-type compound presents a very rigid framework, the umbite-type structure being much more flexible. In both cases, the dehydration process takes place with a reduction in cell volume. Anhydrous tin silicate presents a monoclinic cell whose volume is almost invariant with temperature. K 2 PbSi 3 O 9 is obtained as an amorphous material. The structural characteristics of these phases are related to their ion exchange properties.

A potassium iron zirconium phosphate, K2FeZrP3O12, was synthesized by thermal treatment of a material obtained by the sol–gel method, mixing two aqueous solutions, the first containing KCl, FeCl3 and ZrOCl2, and the second, H3PO4. The crystal structure was refined using powder X-ray diffraction data. The unit cell is cubic, a=10.0554(3) A, space group P213. This compound is the first iron zirconium phosphate described with a langbeinite-type structure.

A novel framework mixed tin–zirconium silicate, K2Sn0.25Zr0.75Si3O9·H2O (1), was synthesized under mild hydrothermal conditions. The unit cell is orthorhombic, a=10.260(2) A, b=13.272(2) A, c=7.174(1) A, space group P212121, Z=4. Isotypic with the mineral umbite, the structural formula may be written as K 2 ( Sn , Zr ){ uB ,1 ∞ 1 }[ 3 Si 3 O 9 ] . In a topotactical process, the K+ ions in compound 1 were replaced by Na+ ions, thus obtaining compound 2: Na2Sn0.25Zr0.75Si3O9·H2O (2), a=10.500(1) A, b=13.354(2) A, c=7.2731(9) A.

A novel layered tin(IV) phosphate, Sn(HPO4)2·(NH3)0.4(H2O)0.6, was synthesized under mild hydrothermal conditions. The unit cell is trigonal, a=4.9751(2) A , c=22.5983(8) A , space group R 3 , Z=3. The interlayer water and ammonia molecules are disordered and were both located on the same crystallographic site. This compound is the first example within the well-known family of α-metal(IV) phosphates of a non monoclinic phase stable at room temperature. The polymorphism of these compounds would explain several of the bibliographical discrepancies detected in the description of its physical–chemical properties.

Powder X-ray diffraction data for π-Ti 2 O(PO 4 ) 2 ·2H 2 O (π-TiP) is indexed in a monoclinic cell [ a =5.067(4), b =10.898(3), c =14.533(8) A, β =96.0(1)°]. Structural correlations with other titanium phosphates are discussed. The reaction of π-TiP with molten MNO 3 (M=Na, K) originates new metal phases with a KTP-type formula, π-M 0.5 H 0.5 TiOPO 4 . These compounds maintain the fibrous morphology of their precursor. The reactions are monitored by thermogravimetric analysis. Thermal decomposition of the novel compounds is described.

The reaction between natural phlogopite, having the idealized formula KMg3(AlSi3O10)(OH)2, and phenylphosphonic acid under soft conditions (24 h, 80 °C, reflux) originated a new layered material of the following idealized composition: [Mg(H2O)2]0.5(AlSi3O6)(O3PC6H5)2·2H2O. The reaction mechanism involves the rupture of the trioctahedral layers of phlogopite and the formation of a new basal spacing of a hydrophobic type that is occupied by phenylphosphonic groups in a pseudomonomolecular arrangement. Simultaneously, the mobile K+ ions become partially substituted by [Mg(H2O)2]2+ groups, a hydrophilic space of the vermiculite type thus being obtained.

Fe(NH(3))(2)PO(4) is synthesized under mild hydrothermal conditions in the presence of urea. The crystal structure is solved for powder X-ray diffraction data. The unit cell is orthorhombic, a = 10.1058(2) Å, b = 6.3676(2) Å, c= 7.5714(2) Å, space group Pnma, Z = 4. The structure consists of a three-dimensional network of FeO(4)N(2) octahedra and PO(4) tetrahedra linked by vertex sharing. Two crystallographically independent ammonia molecules are linked to the iron atom. This compound is the first three-dimensional solid structurally characterized containing Fe-NH(3) bonds.

A potassium zirconium pyrogermanate, K2ZrGe2O7, was synthesized hydrothermally at 180°C from a mixture of zirconium propionate, GeO2, and KOH. The crystal structure was solved from in-house X-ray powder data by direct methods and Fourier analysis. Refinement of the structure was effected by the Rietveld full-pattern technique. The compound is monoclinic, space group C2/c, a=9.9619(2) A, b=5.5578(1) A, c=12.9555(3) A, β=105.169(1)°, Z=4. The structure is remarkably like that of α-zirconium phosphate. Zr(HPO4)2·H2O, except that the layers are crosslinked by the pyrogermanate group to form a three-dimensional lattice. Exchange of the K+ ions is minimal as they are strongly held within the confines of narrow tunnels. The relationship of this newly synthesized pyrogermanate to a sodium zirconium pyrogermanate prepared hydrothermally at 500°C and Na3H(GeO4)2 is discussed.

The proton form of the exchanger Na{sub 2}Ti{sub 2}O{sub 3}(SiO{sub 4}){center_dot}2H{sub 2}O exhibits a high selectivity for Cs{sup +} even in acid solutions. A neutron diffraction study was carried out to locate the position of the exchangeable protons. The structure contains cubane-like Ti{sub 4}O{sub 4} clusters bridged by silicate groups. The acidic proton is located on the cubane oxygens which make them four-coordinate, being bonded to three titaniums and one proton. The unit cell is tetragonal. There are six water molecules per tunnel and two tunnels per unit cell. Thus, the empirical formula is Ti{sub 2}(OH){sub 2}OSiO{sub 4}{center_dot}1.5H{sub 2}O. The water molecules are H-bonded to the framework oxygens and to each other. Although the tunnels are filled with water molecules, framework sites normally occupied by Na{sup +} are empty. The high selectivity for Cs{sup +} apparently stems from the ability to form a thermodynamically stable eight-coordinate complex by replacement of the hydroxyl protons.

The syntheses of α-M(HAsO 4 ) 2 ·H 2 O (M=Ti, Sn and Pb) have been optimized to prepare crystalline single phase materials. The crystal structures of M=Sn, Pb have been refined using X-ray powder diffraction data by the Rietveld method. A combined X-ray and neutron powder data refinement for M=Ti has allowed to obtain a very detailed picture of the structure including the hydrogen-bonding network. The results have been compared with those of the phosphates analogs. In addition, detailed characterization of the samples has been carried out by IR spectroscopy, thermal analysis and powder thermodiffractometry.

Lithium dialkylcuprates react either in a sequential one-pot or in a domino “three-component” fashion with chiral Michael acceptors, like Oppolzer's N-enoyl-2,10-camphorsultams 7 and 11 or ‘Evans’ N-enoyl-4-phenyl-1,3-oxazolidin-2-ones 8 and 13, and N-(methoxycarbonylmethylidene)(4-methoxyphenyl)amine 9 to afford the corresponding cis-3-alkyl-4-methoxycarbonyl-1-(4-methoxyphenyl)azetidin-2-ones 10, 14-15 in overall yields of 40-67% and enantiomeric excesses of 91-99%.

A highly crystalline compound Hf(PO4)(H2PO4)·2H2O (γ-HfP) has been prepared via the partially substituted γ-HfP sodium phase, by the reflux method. Its crystalline structure was solved by X-ray powder diffractometry: monoclinic, space group P21, a = 5.3499(3), b = 6.5949(4), c = 12.3939(8) A, β = 98.594(5)° and Z = 2. The final agreement factors are: Rwp = 0.054, Rexp = 0.031 and RF = 0.033. The compound is isostructural with γ-ZrP and has a layered structure built from PO4 tetrahedra and HfO6 octahedra stacked along the [001] direction. Its intercalation behaviour with n-alkylamines (n = 1–6) and cyclic amines (aniline, benzylamine, cyclohexylamine, piperidine and pyridine) was studied. The intercalation solids obtained present expanded interlayer distances and a general composition Hf(PO4)(H2PO4)·xamine·H2O where x varies from 0.8 to 2.

The photochemical reaction of the adducts Rh2(O2CCH3)3[(C6H4)P(o-ClC6H4)Ph]· (P(p-XC6H4)3) (X=H, Me, Cl), yield the compounds Rh2(O2CCH3)2(η2-O2CCH3)[(p-XC6H3)P (p-XC6H4)2](η2-PCCl), (PCCl=P(o-ClC6H4)Ph2) in a ligand rearrangement reaction that involves activation of CH and RhC bonds. The factors that favour this process are studied by carrying out photochemical reactions with different phosphines. The structures of Rh2(O2CCH3)2(η2-O2CCH3) [(C6H4)PPh2](η2-PCCl) has been determined by X-ray diffraction. Mr=1321.1, orthorhombic, space group Pbcn, a=20.339(8), b=20.07(6), c=23.07(3) A , V=9413(3) A 3 , Z=8, D x =1.86 g cm −3 . Mo Kα radiation (graphite crystal monochromator, λ=0.071073 A ), μ(Mo Kα) = 13.83 cm−1, F(000)=5280, T=293 K. Final conventional R factor=0.062 for 4889 ‘observed’ reflections and 500 variables. The compound contains three bridging ligands, two acetates and one metalated triphenylphosphine, and two chelating ligands, one acetate and one PCCl that acts as a P,Cl ligand, taking one equatorial (P) and one axial (Cl) coordination site. The axial RhCl bond distance is 2.573(4) A.

A). Searching for possible superdense carbon allotropes, we have found three structures (hP3, tI12, and tP12) that have significantly greater density. The hP3 and tP12 phases have strong analogy with two polymorphs of silica (β-quartz and keatite), while the tI12 phase is related to the high-pressure SiS2 polymorph. Furthermore, we found a collection of other superdense structures based on the motifs of the aforementioned structures, but with different ways of packing carbon tetrahedra, and among these the hP3 and tI12 structures are the densest. At ambient conditions, the hP3 phase is a semiconductor with the GW band gap of 3.0 eV, tI12 is an insulator with the band gap of 5.5 eV, while tP12 is an insulator, the band gap of which is remarkably high (7.3 eV), making it the widest-gap carbon allotrope. These allotropes are metastable and have comparable to diamond or slightly higher bulk moduli; their Vickers hardnesses are calculated to be 87.6 GPa for hP3, 87.2 GPa for tI12, and 88.3 GPa for tP12, respectively, thus making these allotropes nearly as hard as diamond (for which the same model gives the hardness of 94.3 GPa). Superdense carbon allotropes are predicted to have remarkably high refractive indices and strong dispersion of light.

A novel titanium(IV) phosphate, (NH4)0.79(P1.14Ti0.86)O3.93(OH)2.07, has been prepared using hydrothermal synthesis with H3PO3, TiCl4, H2O2 and (NH2)2CO; powder X-ray structure determination reveals the P(V) as hexa-coordinated.

The reaction between 2-aminobuta-1,3-dienes and pentacarbonyl-[1-methoxy-frans-3-(2-furyl)-prop-2-enylidene]-chromium(0) takes place at room temperature leading with total regio- and stereo-selectivity to functionalized seven-membered carbocycles with good yields.

The proton form of the exchanger Na{sub 2}Ti{sub 2}O{sub 3}(SiO{sub 4}){center_dot}2H{sub 2}O exhibits a high selectivity for Cs{sup +} even in acid solutions. A neutron diffraction study was carried out to locate the position of the exchangeable protons. The structure contains cubane-like Ti{sub 4}O{sub 4} clusters bridged by silicate groups. The acidic proton is located on the cubane oxygens which make them four-coordinate, being bonded to three titaniums and one proton. The unit cell is tetragonal. There are six water molecules per tunnel and two tunnels per unit cell. Thus, the empirical formula is Ti{sub 2}(OH){sub 2}OSiO{sub 4}{center_dot}1.5H{sub 2}O. The water molecules are H-bonded to the framework oxygens and to each other. Although the tunnels are filled with water molecules, framework sites normally occupied by Na{sup +} are empty. The high selectivity for Cs{sup +} apparently stems from the ability to form a thermodynamically stable eight-coordinate complex by replacement of the hydroxyl protons.

A sodium niobium(V) tetrasilicate, Na2H(NbO)Si4O11·1.25H2O (1), was synthesized hydrothermally at 190 °C from a mixture of silicic acid, NaOH, NbCl5, and H2O2 and added hydrochloric acid. The successive treatment of 1 with nitric acid yielded HNb(H2O)Si4O11·H2O (2). Contact of 2 with cesium hydroxide solutions converted it to the partially exchanged Cs+ phase Cs0.66H0.33Nb(H2O)Si4O11 (3). The three structures were solved from X-ray powder diffraction data. All compounds crystallize in the monoclinic space group P21/m with Z = 2, containing the Si8O2212- anion. This new silicate anion type is related to the Si4O116- unit, which is present in the amphibole series. The difference between both anion types lies in the chain periodicity: two for amphiboles or four for the new niobium silicates. These niobium silicates have framework structures enclosing tunnels in which the alkali cations reside.

Interest in Fe(ND3)2PO4, one of the first three-dimensional structurally linked solids forming Fe–ND3 bonds, has been renewed recently due to the observation of structural and magnetic phase transitions. This paper reports powder neutron diffraction experiments which show that Fe(ND3)2PO4 crystallizes at room temperature in an orthorhombic (Pnma) crystal structure, but that below Tt = 226(5) K the crystal progressively adopts a monoclinic (P21/n) structure via a continuous phase transition, as observed from heat capacity measurements in the temperature range 250–100 K. In addition, neutron diffraction experiments suggest that the magnetic structure is non-collinear with an incommensurate propagation vector kinc = (1/2- τ, ∼, 0, τ, with τ ∼ 0.04 reciprocal lattice units (rlus), and that the magnitude of the Fe(III) magnetic moments is close to μFe = 4.5 μB at T = 2 K, describing a helimagnetic arrangement. To the best of our knowledge, this is an unprecedented magnetic ordering in an iron phosphate lattice. We argue that the proposed magnetic ordering can be explained by means of a model of superexchange interactions involving Fe–O–P–O–Fe paths., This work has been carried out with the financial support of FEDER-MEC (MAT2006-01997, MAT2008-06542-C04-03, and Factoría Española de Cristalización – Consolider Ingenio 2010).

Reaction between [Fe(CCMetBu)(η-C5H5)(dppm)][CF3SO3] (dppm = bis(diphenylphosphino) methane) and NaOMe at − 20°C resulted in the deprotonation of dppm followed by the intramolecular nucleophilic attack of the methanide group on the vinylidene α-carbon to give [ Fe(CCMe t Bu)(η-C 5 H 5 )(Ph 2 P CCMe t Bu)(η-C 5 H 5 ){(Ph 2 P) 2 C H}]. An X-ray single-crystal structure determination shows that the complex contains a novel 1-ferra-2,4-diphosphabicyclo[1.1.1]pentane ring system.

Microcrystals of the first ammonium-thorium phosphates, (NH4)2Th(PO4)2·H2O (tetragonal, I41/amd, a = 7.0192(4) A, c = 17.9403(8) A) and NH4Th2(PO4)3 (monoclinic, C2/c, a = 17.880(6) A, b = 6.906(1) A, c = 8.152(2) A, β = 104.39(2)°) were hydrothermally obtained from a Th(NO3)4-CO(NH2)2-H3PO3-H2O system (T = 180 °C). In both cases, the structure consists of a three-dimensional framework with PO4 tetrahedra coordinated to Th atoms (ThOn polyhedra, where n = 8 or 9, for the tetragonal or monoclinic phase, respectively). The ammonium ions (and water molecules) are located in the tunnels.

Fe(H{sub 2}PO{sub 4})(H{sub 2}P{sub 2}O{sub 7}).C{sub 5}H{sub 5}N, a new iron(III) phosphate with an open-framework has been synthesized hydrothermally using pyridine as organic template. The crystal structure was solved ab initio using conventional powder X-ray diffraction data. The unit cell is orthorhombic, a=9.5075(2), b=10.1079(1), c=13.3195(2) A, space group P2{sub 1}2{sub 1}2{sub 1}, Z=4. The structure consists of FeO{sub 6} octahedra joined by H{sub 2}PO{sub 4} and H{sub 2}P{sub 2}O{sub 7} groups forming linear chains interconnected by hydrogen bonding to give rise to a supramolecular framework enclosing tunnels in which the pyridine molecules reside. - Graphical abstract: The low temperature hydrothermal synthesis offers many possibilities in the preparation of new materials with mixed octahedral-tetrahedral open-frameworks. Fe(H{sub 2}PO{sub 4})(H{sub 2}P{sub 2}O{sub 7}).C{sub 5}H{sub 5}N is constituted by linear chains of FeO{sub 6} octahedra joined through of both dihydrogenphosphate and dihydrogendiphosphate bridges, interconnected by hydrogen bonds, originating channels where the pyridine molecules are located.

Binary oxides of elements belonging to groups 13-15 are of special relevance from a fundamental point of view as well as because of their technological applications as a basis in zeotypes, glasses, or semiconductors. Aluminum oxide, Al2O3, crystallizes in the corundum structure, which is stable at low and high pressures, with the Al showing octahedral coordination. Silicon oxide, SiO2, crystallizes in phases with tetrahedral Si coordination at low pressures as alpha-quartz, but at high pressures, octahedral coordination is stable in the stishovite polymorph. The only known binary phosphorus(V) oxides have tetrahedral P coordination. We have studied the stability of different phases of P2O5 at high pressure, applying density functional theory methodology within the local density and generalized gradient approximations and a plane-wave basis set. Our results indicate that the most stable form of P2O5 at high pressure could be one with hexacoordinated phosphorus. All of the high-pressure phases of Al, Si, and P can be described as a different linking of the same rutile-type blocks.

Microcrystals of Th(HPO 4) 2.H 2O were hydrothermally obtained from a Th(NO 3) 4-CO(NH 2) 2-H 3PO 3-H 2O system ( T = 180 masculineC). The structure [orthorhombic, Pbca, a = 9.1968(2) A, b = 18.6382(2) A, c = 8.7871(2) A], unlike alpha-Zr(HPO 4) 2.H 2O-type layered compounds, consists of a three-dimensional framework with PO 4 tetrahedra coordinated to Th atoms. The water molecule is also coordinated to the Th atom and projected toward small channels running along the directions of the a and c axes. The ThO 6O(w) environment could be described as a highly distorted pentagonal bipyramid.

Microcrystals of Th(HPO4)2·H2O were hydrothermally obtained from a Th(NO3)4−CO(NH2)2−H3PO3−H2O system (T = 180 ºC). The structure [orthorhombic, Pbca, a = 9.1968(2) Å, b = 18.6382(2) Å, c = 8.7871(2) Å], unlike α-Zr(HPO4)2·H2O-type layered compounds, consists of a three-dimensional framework with PO4 tetrahedra coordinated to Th atoms. The water molecule is also coordinated to the Th atom and projected toward small channels running along the directions of the a and c axes. The ThO6O(w) environment could be described as a highly distorted pentagonal bipyramid., We express our thanks for financial support from the Spanish Ministerio de Educación y Ciencia (Grants MAT2006-13548-C02-02 and MAT2006-01997 and Factoría de Cristalización, Consolider Ingenio 2010) and the Gobierno del Principado de Asturias (PCTI 2006–2009). The authors are also grateful to the SpLine Beamline staff for support during the powder XRD experiments and for financial support from MEC and CSIC (Intramural 2004 5 OE 292) to carry out the synchrotron powder XRD experiments.

Th2(PO4)2(HPO4)·H2O was synthesized under wet hydrothermal conditions starting from a mixture of H3PO3 and Th(NO3)4·5H2O. The crystal structure was solved by powder X-ray diffraction data. The unit cell parameters are a = 6.7023(8) A, b = 7.0150(8) A, c = 11.184(1) A, β = 107.242(4)°, space group P21, and Z = 2. The structure consists of layers of both thorium atoms and PO4 groups, alternating with a layer formed by HPO4 entities and water molecules. By thermal treatment, this compound turns into Th4(PO4)4P2O7, a ceramic already described in the field of the immobilization of tetravalent actinides.

Polycrystalline intercalated TiMxH2-nx(PO4)2·yC3H7NH2·wH2O compounds with transition metal (TM) ions (Mn+ = Co2+, Ni2+, Fe3+ or Cr3+) have been prepared by means of an indirect route and characterised using X-ray diffraction, scanning electron microscopy, chemical and thermal analysis, X-ray absorption and magnetic measurements. These novel pillared layered materials, which were obtained from the monoclinic (P21/c space group) alpha-Ti(HPO4)2·H2O phase, lose its crystallinity after intercalation. However, all the TM ions are octahedrally surrounded by 6 oxygen atoms, although the X-ray absorption spectra evidence a clear dependence on the temperature. Surprisingly, all the materials behave as paramagnetic down to 1.5 K, but they exhibit different colors, which means that they are optically active (Co2+: violet; Ni2+: pale green; Fe3+: yellow; Cr3+: dark green)., This work was supported by MEC (Spain), Re-search Projects Nos. MAT2002-04178-C04 and MAT2003-02940

The reaction between 2-aminobuta-1,3-dienes and pentacarbonyl-[1-methoxy-frans-3-(2-furyl)-prop-2-enylidene]-chromium(0) takes place at room temperature leading with total regio- and stereo-selectivity to functionalized seven-membered carbocycles with good yields.

A sodium niobium(V) tetrasilicate, Na(2)H(NbO)Si(4)O(11).1.25H(2)O (1), was synthesized hydrothermally at 190 degrees C from a mixture of silicic acid, NaOH, NbCl(5), and H(2)O(2) and added hydrochloric acid. The successive treatment of 1 with nitric acid yielded HNb(H(2)O)Si(4)O(11).H(2)O (2). Contact of 2 with cesium hydroxide solutions converted it to the partially exchanged Cs(+) phase Cs(0.66)H(0.33)Nb(H(2)O)Si(4)O(11) (3). The three structures were solved from X-ray powder diffraction data. All compounds crystallize in the monoclinic space group P2(1)/m with Z = 2, containing the Si(8)O(22)(12-) anion. This new silicate anion type is related to the Si(4)O(11)(6-) unit, which is present in the amphibole series. The difference between both anion types lies in the chain periodicity: two for amphiboles or four for the new niobium silicates. These niobium silicates have framework structures enclosing tunnels in which the alkali cations reside.