Pilar Pertierra

Layered acid arsenates α-M(HAsO4)2·H2O (M=Ti, Sn, Pb): synthesis optimization and crystal structures

Abstract 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.

Photochemical ligand rearrangement in dirhodium(II) compounds. Structure of Rh2(O2CCH3)2(η2-O2CCH3)[(C6H4)PPh2] (η2-PCCl)(PCClP-ClC6H4)Ph2

Abstract 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.

An expeditious stereoselective synthesis of functionalized seven-membered carbocycles by reaction of 2-aminobuta-1,3-dienes with vinylchromium fischer type carbenes

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.

Hydrothermal synthesis and structural characterization of framework microporous mixed tin–zirconium silicates with the structure of umbite

Abstract 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.

Synthesis and crystal structure of thorium bis(hydrogenphosphate) monohydrate.

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.

Structural and magnetic phases of Fe(ND3)2PO4

Polycrystalline samples of Fe(ND3)2PO4 were prepared by means of a hydrothermal route and characterized using powder x-ray diffraction, scanning electron microscopy, chemical and thermal analysis, magnetic measurements, specific heat and neutron diffraction experiments. This material orders within an orthorhombic (Pnma space group) crystal structure at room temperature, but below 220 K the crystal structure changes towards a monoclinic P 21/n structure through a phase transition with almost no latent heat. Furthermore, the magnetic cell at 2 K is twice the size of the crystallographic cell observed at 80 K. The magnetic structure associated with the Fe(III) ions is thus commensurate with the crystal lattice having a propagation vector , the magnetic moments lying in the yz plane of the crystallographic cell.

Phosphorous Acid and Urea: Valuable Sources of Phosphorus and Nitrogen in the Hydrothermal Synthesis of Ammonium-Thorium Phosphates

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.

Hydrothermal synthesis and X-ray powder structure determination of a novel layered tin(IV) phosphate, Sn(HPO4)2·(NH3)0.4(H2O)0.6

Abstract 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.

An Asymmetric Domino Three-Component Synthesis of β-Lactams

Lithium dialkylcuprates react either in a sequential one-pot or in a domino “three-component” fashion with chiral Michael acceptors, like Oppolzers 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%.

Theoretical study of P2O5 polymorphs at high pressure: hexacoordinated phosphorus.

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.