Structure cristalline de (NH4)2PO3H,H2O: Stereochimie de l'Ion PO3H2− et ses relations avec PO3F2− et SO32−

(NH₄)₂PO₃H, H₂O crystallizes in the monoclinic system, space group P2₁/c, with a = 6.322(1) Å, b = 8.323(1) Å, c = 12.676(1) Å, β = 98.84(1) and Z = 4. The structure was refined to R = 0.022 based on 853 independent X-Rays intensities. Improved dimensions of the tetrahedral PO₃H^2? ion have been obtained: P?H = 1.34(2) and P?O = 1.514(2) Å. The geometry of this ion is compared with that of PO₃F^2? and SO₃^2? ions and we find a decrease of the volume: V_F? > V_H+ > V_{lone pair}.     

Etude structurale de derives du fer carbonyle: II. Structure cristalline et moleculaire d'un complexe du fer carbonyle avec la 2-mercapto-pyridine,C5H4N(CO)6Fe2-μ4-S-Fe2(CO)6SC5H4N

The crystal and molecular structure of a complex prepared by reaction between Fe₃(CO)₁₂ and 2-mercaptopyridine and of formula C₅H₄N(CO)₆Fe₂-μ₄-S-Fe₂(CO)₆SC₅H₄N has been determined by a single-crystal X-ray study. The compound crystallises in the monoclinic space group $\text{P}\text{2}{}_1\text{n}$, with Z = 4. Data were collected on a NONIUS CAD-4 automatic diffractometer. The structure was solved both by the heavy-atom method and direct methods and refined to R and R″ values of 0.041 and 0.038 for 2089 independent reflections. The molecule contains four Fe(CO)₃ groups with two ironiron bonds bridged in a different way, and a sulphur atom tetrahedrally coordinated to the four iron atoms.     

Structure cristalline et spectres Raman polarises de Na1,5Sm8,5(SiO4)6FO

The silicated apatite Na_1.5Sm_8.5(SiO₄)₆FO crystallizes in the hexagonal system, with a=9.4761(6) Å, c=6.9484(4) Å cell parameters, P6₃/m space group, and Z=1. The samarium distribution over the 4f and 6h positions is not uniform. Due to their polarizability higher than the one of sodium, samarium ions mainly set on the 6h position, but their occupation of this position rate is limited by the valence required for fluorine. The Raman spectra, collected in various polarizations, are consistent with the proposed space group. An attribution of several external modes is given by comparison with the spectra of Ca₆Sm₂Na₂(PO₄)₆F₂, Ag₂Pb₈(PO₄)₆, Na₂Pb₈(PO₄)₆ and Ca₁₀(PO₄)₆F₂ (fluorapatite).     

Enthalpie de formation de la whitlockite Ca18Mg2H2(PO4)14

Pure and well crystallised whitlockite Ca₁₈Mg₂H₂(PO₄)₁₄ has been synthesized by precipitation from the magnesium and calcium nitrates and the diammonic phosphate. The product of the reaction has been characterized by X-ray diffraction, IR spectroscopy and chemical analysis. Using differential conduction calorimeters the enthalpies of solution of the whitlockite and of a mixture of the solid reactants - the tricalcium, the trimagnesium and the dicalcium phosphates - have been measured at 25°C for various concentrations of solid in a 46 wt% nitric acid solution. A combination of the enthalpies of solution with the enthalpies of formation of the reactants allows us to determine the standard enthalpy of formation of the whitlockite. The value deduced, -27,93·10³kJ mol^-1, is compared to the standard enthalpies of formation of the trimagnesium and the tricalcium phosphates. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sur les carbonates basiques de fer (III): II. Préparation,radiocristallographie et spectres IR. du (NH4)2Fe2(OH)4(CO3)2 · H2O

The obtention of the crystalline basic carbonate of iron (III) and ammonium, (NH₄)₂Fe₂(OH)₄(CO₃)₂ · H₂O, is described and its formula is established by chemical analysis and infrared spectroscopy. The powder X-ray diagram could be indexed tetragonally leading to a body centred elementary cell with a = 12,04 ± 0,02 Å and c = 6,62 ± 0,01 Å. The infrared spectra show that in the CO groups either one oxygen atom is linked to one iron atom or, rather, two oxygen atoms are linked to two iron atoms. The symmetry of the NH groups is lower than C_3v. The OH-groups are linked by hydrogen bonds of 2,75 Å. Two sorts of OH-groups can be distinguished, with a radius of approximately 1,34 Å and 1, 48 Å, respectively. The iron atoms are octahedrally coordinated by oxygen atoms, but either the octahedra are deformed or the iron atoms are in part coordinated tetrahedrally.     

Preparation et proprietes physico-chimiques de l'alanate de magnesium Mg(AlH4)2

Résumé L'alanate de magnésium Mg(AlH₄)₂ désolvaté a été obtenu avec une pureté satisfaisante. La décomposition thermique a été étudiée par thermogravimétrie sous pression réduite (10^–3 torr). La capacité calorifique molaire à 298 K ainsi que l'enthalpie de formation ont été déterminées avec un microcalorimètre Calvet.C _p Mg(AlH₄)₂=32.5 cal·mol^–1·K^–1;H _fMg(AlH₄)₂=–19.2 kcal· mol^–1

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Solvent-free Mg(AlH₄)₂ has been prepared with good purity. Thermogravimetry has been used to investigate the thermal decomposition of Mg(AlH₄)₂ under low pressure (10^–3 torr). The molar heat capacity at 298 K and the heat of formation have been measured with a CALVET microcalorimeter.C _p Mg(AlH₄)₂=32.5 cal·mol^–1·K^–1 H _fMg(AlH₄)₂=–19.2 kcal·mol^–1

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Zusammenfassung Lösungsmittelfreies Mg(AlH₄)₂ wurde mit befriedigender Reinheit hergestellt. Scine thermische Zersetzung wurde durch Thermogravimetrie bei niedrigem Druck (10^–3 torr) untersucht. Die molare Wärmekapazität bei 298 K und die Bildungswärme wurden mit einem Calvet Mikrokalorimeter gemessen.C _p Mg(AlH₄)₂=32.5 cal·mol^–1·K^–1;H _f Mg(AlH₄)₂=–19.2 kcal· mol^–1

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Mg(AlH₄)₂, . Mg(AlH₄)₂ (10^–3 ) . 298 . C_pMg(AlH₄)₂=32.5 ^–1. ^–1 H _fMg(AlH₄)₂=–19.2 ^–1.

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Ce travail a été effectué dans le cadre d'un contrat de recherches passé par le Laboratoire de Chimie Minérale avec la Direction des Recherches et Moyens d'Essai. Nous remercions bien vivement cet organisme de l'aide qu'il a nous apportée.     

Sur L'Existence d'un Intermediaire Reactionnel Entre Phosphate et Pyrophosphate Acide de Potassium: Cas de K2H8(PO4)2P2O7

On the Existence of Intermediate Reaction Products of Potassium Hydrogen Phosphate and Diphosphate: K₂H₈(PO₄)₂P₂O₇ The crystal structure of K₂H₈(PO₄)₂P₂O₇ has been determined from diffractometer data obtained using MoKα radiation. The space group is Pca2₁ with a = 9.364(2), b = 7.458(2) and c = 19.560(2) Å, V = 1 366.0 ų; d_m = 2.17(1) g/cm³. Z = 4 · μ(MoKα) = 12.47 cm^?1. The structure was solved by direct methods. The crystal structure was refined to R = 0.025 for 416 independent reflexions. Two kinds of PO₄ exist and the mean value of P? O is 1.55(2) Å for one and 1.53(2) Å for the other. In P₂O₇ the angle P? O? P is 135(1)°. The distances P? O of bridge are 1.59(2) and 1.57(2) Å the mean value of P? O in terminals ? PO₃ is 1.51(2) Å. The coordination numbers of the potassium ions are nine and eight. K₂H₈(PO₄)₂P₂O₇, compound with mixed anion PO₄/P₂O₇ may be considered as reactional intermediary between acid orthophosphate and pyrophosphate.