Jacques Roziere

The isomorphous acid salts α-Zr(HPO4)2.H2O, α-Ti(HPO4)2.H2O and α-Zr(HASO4)2.H2O : Comparative thermochemistry and vibrational spectroscopy

Abstract A set of isomorphous acid salts of ideal general formula α-M IV (HXO 4 ) 2 · H 2 O [α-zirconium phosphate (α-ZrP), α-titanium phosphate (α-TiP) and α-zirconium arsenate(V) (α-ZrAs)] has been investigated. In the case of α-ZrP, different preparative techniques were used to yield samples of differing crystallinity. Sample characterisation was by X-ray powder diffraction, thermochemical techniques (TG and DSC), and optical spectroscopies (infrared and Raman). Thermochemical findings included (i) phase transitions in anhydrous TiP occur at higher temperature than for ZrP, (ii) condensation of the acid anions at lower temperature for the arsenate than for the phosphates, (iii) dependence of temperatures of thermal events in α-ZrP on the crystallinity of the material. Bands and lines occurring in the optical spectra of these materials have been discussed and assigned.

Neutron diffraction study of (Et/sub 4/N)/sup +/(Cr/sub 2/(CO)/sub 10/(. mu. /sub 2/-H))/sup -/: a (M/sub 2/(CO)/sub 10/(. mu. /sub 2/-H))/sup -/ monoanion with a pseudo D/sub 4h/ nonhydrogen geometry together with a disordered, bent symmetric metal--hydrogen--metal bond

The results of a single-crystal neutron diffraction study of the chromium-hydrogen-chromium bond in (Et/sub 4/N)/sup +/(Cr/sub 2/(CO)/sub 10/(..mu../sub 2/-H))/sup -/ was reported. The Cr-H-Cr bond in the (Cr/sub 2/(CO)/sub 10/(..mu../sub 2/-H))/sup -/ monoanion of the tetraethylammonium salt was found to be non-linear with the bridging hydrogen atom randomly disordered between two centrosymmetrically related sites each equidistant from the two chromium atoms and displaced ca. 0.3 A from the crystallographic center of symmetry. (DDA)

Metal alkoxides with polymerizable ligands: synthesis and molecular structure of [Nb4(μ-O)4(μ, η2-O2CMe-CH2)4(OPri)8]

Abstract The reaction between [Nb(OPr i ) 5 ] 2 and methacrylic acid [CH 2 C(CH 3 )CO 2 H-McOH], and subsequent controlled microhydrolysis, gave [Nb 4 (μ-O) 4 (μ, η 2 -Mc) 4 (OPr i ) 8 ] which was characterized by X-ray diffraction. The compound is based on a planar Nb 4 O 4 core with terminal isopropoxide ligands, while the functional car☐ylates act as bridging chelating ligands. The Nb-O bond lengths vary from 1.840(3) to 2.203(4)A˚and follow the order Nb-OR ∼ Nb-O

The crystal structure of RbHSeO4: A neutron diffraction study of the paraelectric phase

Abstract The structure of the paraelectric phase of RbHSeO 4 has been determined at 387 K by neutron diffraction. The structure consists of chains of hydrogen bonded SeO 4 groups extending along the crystallographic b axis. Two different hydrogen bonds have been characterized, with Oue5f8O distances of 2.524(4) and 2.583(3) A. In the shorter Oue5f8Hue5f8O hydrogen bond the hydrogen atom is disordered, suggesting that the ordering of hydrogen participates directly in the phase transition to the ferroelectric phase.

Development of Covalently Cross-linked and Composite Perfluorosulfonic Acid Membranes

A straight forward approach to increase proton conductivity at relatively dry conditions is to increase the number of sulfonic acid groups in the polymer. Although various PFSAs of significantly lower EW can be prepared, the limitation of this approach is that the polymer and membrane properties are also affected, with membranes showing increased water uptake and dimensional swelling. Our approach has been to develop a series of approaches for the cross-linking of PFSAs in order to improve membrane mechanical properties and reduce membrane swelling in the presence of water. Novel side-chain component multifunctional monomers have been developed that are cross-linkable after membrane fabrication. The result of this approach is that a suite of polymers have been synthesized that, after membrane casting and cross linking show excellent proton conductivity, even under conditions of elevated temperature and <50% RH.

Infrared evidence for the diaquooxonium ion in crystallized HNO3,3H2O and HClO4,3H2O

Abstract The existence of asymetric H 7 O 3 + ions in crystalline trihydrates of perchloric and nitric acids, first detected by X-ray diffraction is further confirmed by vibrational spectroscopy. The spectra are consistent with a H 3 O + central pattern complexed by two water molecules through short and asymetric hydrogen bonds.

Niobium pinacolate complexes: synthesis and molecular structures of Nb3(μ-O)2(μ, η2-OCMe2CMe2O)2(η2-OCMe2CMe2O)4H and of Nb4(μ-O)2(μ3-O)2(μ, η2-OCMe2CMe2O)2(OPri)8

Abstract The reactions between niobium alkoxides [Nb(OR)5]2 (R=Pri, Et) and pinacol HOCMe2CMe2OH (pinH2) were investigated in different stoichiometries in toluene at room temperature. Nb4O4(pin)2(OPri)8 (1), [Nb2O(pin)4H2(OPri)2]m (2) and Nb3O3(pin)6H (3) were isolated. The various products were characterized by elemental analyses, FT-IR and 1H NMR spectroscopy and by X-ray diffraction for 1 and 3. The niobium atoms are all six-coordinated. The Nb–O bond lengths vary according to Nb–OPri

Acid sulphates of trivalent metals: A new class of protonic conductors☆

Abstract A novel class of layer structured proton conductors HM (III) (SO 4 ) 4 · n H 2 O, n =1 or 4, in which hydrated proton species are intercalated in an anionic macrostructure, has been studied. Protonic conduction properties are discussed in relation to the nature of the intercalated species and the crystal structure.

Etude par spectroscopie de vibration des hexahydroxodialuminate et digallate de potassium

Resume Letude des spectres i.r. et Raman de K AlO 2 , 1,5 H 2 O et de K GaO 2 , 1,5 H 2 O permet detablir la presence des ions [Al 2 O(OH) 6 ] 2− et [Ga 2 O(OH) 6 ] 2− . Elle confirme une etude anterieure de radiocristallographie sur lhexahydroxodialuminate de potassium. Ces ions sont constitues par des tetraedres MO 4 accoles par un sommet. Aucune difference notable entre les quatre liaisons Mue5f8O na pu etre mise en evidence par spectroscopie. Par contre, le spectre des vibrateurs OD du cristal K MO 2 , 1,5 D 2 O dilue dans K MO 2 , 1,5 H 2 O permet de differencier seulement trois liaisons Oue5f8D inegales. Ceci confirme la presence dun element de symetrie cristallographique passant par latome doxygene central du pont Mue5f8Oue5f8M. Les distances Oue5f8H…O deduites des frequences v (OH) sont tout a fait en accord avec les plus courtes distances observees entre atomes doxygene de motifs M 2 O 7 differents. A linterieur dun meme motif, labsence de couplage intertetraedres a facilite letude des vibrations des groupes MO 3 . Cette etude permet de montrer que la force des liaisons Mue5f8O augmente lorsquon substitute le gallium a laluminium. Cette evolution a ete reliee a laugmentation des frequences δ(OH) et a la diminution des frequences v (OH).

Layered proton conducting trivalent metal acid sulphates: intercalation reactions, characterisation by incoherent inelastic neutron scattering and exafs spectroscopies

Abstract Members of the series of acid salts HM(III)(SO 4 ) 2 · n H 2 O, n =1 or 4, M(III)=Al, Fe, In, etc., are protonic conductors ( σ =10 -4 -10 -5 ω -1 cm -1 at 25° C ) of pronounced two-dimensional structure. Hydrated proton species intercalated between the anionic layers [M(SO 4 ) 2 2H 2 O] - n have been identified by incoherent inelastic neutron scattering (IINS) spectroscopy. HFe(SO 4 ) 2 ·4H 2 O is a promising ion exchange and intercalation agent. The products of its redox reactions with lithium, sodium, ammonium and zinc ions have been investigated by IINS and extended X-ray absorption fine structure spectroscopies.