Structure Cristalline du Phosphite Acide de Calcium,Ca(HPO3H)2 · H2O

Crystal Structure of Calcium Hydrogenphosphite Monohydrate, Ca(HPO₃H)₂ · H₂O Ca(HPO₃H)₂ · H₂O is triclinic, space group P1 , with a = 7.007(1), b = 8.100(1), c = 6.773(1) Å, α = 84.92(1), β = 95.72(2) and γ = 112.00(1)°; V = 354.1 ų, Z = 2; ?_x = 2.251 g/cm³ and ?_ob = 2.21(1) g³/cm³. The structure was refined to R = 0.019 for 1640 independent reflections. HPO₃H^? ions are linked together by hydrogen bonds (with acid hydrogen atoms) to form parallelograms. Chains of parallelograms are parallel to c axis. The coordination number of the calcium ion is seven; the mean values of Ca? O is 2.409 Å.     

Structure cristalline et polymorphisme du nitrate de cadmium anhydre

Cd(NO₃)₂ undergoes a phase transition at 160°C. The high temperature form is cubic and isomorphic with M(NO₃)₂ (M = Ba, Ca, Sr, Pb). The crystal structure of the low temperature phase has been solved by X-ray diffraction at 20°C, using 774 independent reflections collected with a 4-circle diffractometer. The dimensions of the orthorhombic unit cell are: $\text{a ? c = 7.5073 (14)}$ Å, b = 15.3692 (35) Å, Z = 8, space group Pca2₁. The structure has been refined to the final weighted R = 0.044. The cadmium atoms are nearly in a face-centered arrangement. Each cadmium is octahedrally surrounded by six oxygen, the CdO distances varying from 2.34 to 2.46 Å. Each nitrate group belongs through its three oxygens to three different octahedra. The structural change cubic Cd(NO₃)₂ → orthorhombic Cd(NO₃)₂ is characterized by a small rotation of NO₃ groups in their plane; the face-centered array of cadmium atoms is only slightly modified. The coordination of cadmium atoms changes from 12 to 6, and the approximate doubling of parameter (b) as well as the difference of symmetry can be explained by two different directions of rotation of the NO₃ groups situated in the same plane.     

Structure cristalline du metatitanate de thallium Tl2TiO3

A thallium titanate oxide Tl₂TiO₃ has been prepared. It is orthorhombic, space groupPnam, with unit cell dimensions a = 12.41 A?,b = 9.615 A?,c = 3.752 A?. The structure contains double chains of edge sharing TiO₅ trigonal bipyramids, in the z direction. In this compound, thallium I has a stereochemically active lone pair. There are four oxygens bonded to thallium, all to one side.     

Etude cristallochimique de derives du chrome(0) : I. Structure cristalline et moleculaire du benzoate de methyle chrome dicarbonyle thiocarbonyle

The crystal and molecular structure of methylbenzoatechromium dicarbonyl thiocarbonyl has been determined by a single-crystal X-ray study. The compound crystallizes with two molecules in a unit cell of symmetry P$\text{1}$, with the following parameters: triclinic system, a = 7.108(3), b = 10.340(4), c = 8.523(3) Å; α = 89.75(6), β = 95.89(4), γ = 105.50(4)°; V = 601 ų; d_m = 1.57 ± 0.05, d_c = 1.56. The structure has been refined to R and R″ values of 0.030 and 0.038 respectively, for 1963 independent reflections. The main feature of the molecule is the C_s symmetry of the Cr(CO)₂CS group with a CrC(S) bond length of 1.792(2) Å, shorter than the CrC(O) bond length, mean: 1.849(3) Å.     

K6[Fe8.27(HPO3)12]: a new mixed‐valence iron phosphite

The title compound, hexapotassium octairon(II,III) dodecaphosphonate, exhibiting a two‐dimensional structure, is a new mixed alkali/3d metal phosphite. It crystallizes in the space group Rm, with two crystallographically independent Fe atoms occupying sites of m (Fe1) and 3m (Fe2) symmetry. The Fe2 site is fully occupied, whereas the Fe1 site presents an occupancy factor of 0.757 (3). The three independent O atoms, one of which is disordered, are situated on a mirror and all other atoms are located on special positions with 3m symmetry. Layers of formula [Fe₃(HPO₃)₄]²⁻ are observed in the structure, formed by linear Fe₃O₁₂ trimer units, which contain face‐sharing FeO₆ octahedra interconnected by (HPO₃)²⁻ phosphite oxoanions. The partial occupancy of the Fe1 site might be described by the formation of two [Fe(HPO₃)₂]⁻ layers derived from the [Fe₃(HPO₃)₄]²⁻ layer when the Fe1 atom is absent. Fe²⁺ is localized at the Fe1 and Fe2 sites of the [Fe₃(HPO₃)₄]²⁻ sheets, whereas Fe³⁺ is found at the Fe2 sites of the [Fe(HPO₃)₂]⁻ sheets, according to bond‐valence calculations. The K⁺ cations are located in the interlayer spaces, between the [Fe₃(HPO₃)₄]²⁻ layers, and between the [Fe₃(HPO₃)₄]²⁻ and [Fe(HPO₃)₂]⁻ layers.     

Pseudoasymetrie dans la serie du benchrotrene II. Structure cristalline de la forme pseudoasymetrique F 144° des glycols ortho-substitutes (OC)3CrC6H4(CHOHCH3)2

The crystalline structure of one of the pseudoasymmetric forms of the benchrotrenic glycols 1,2-(CHOHCH₃)₂C₆H₄Cr(CO)₃ (m.p. 144° C) has been determined by X-ray diffraction to provide a complete identification of these isomeric glycols.