Jean-Pierre Wignacourt

Complexes of cobalt(II), nickel(II) and copper(II) with a thia ligand; 2,5-bis(2-pyridyl)-1,3,4-thiadiazole: structural identification

Abstract A heterocycle, previously untested as a polydentate ligand, 2,5-bis(2-pyridyl)-1,3,4-thiadiazole, namely bptd, has been found to form the monomeric complexes, Co(bptd)2(H2O)2(NO3)2 (I), Ni(bptd)2(H2O)2(ClO4)2 (II), Co(bptd)2(H2O)2(ClO4)2 (III), and Cu(bptd)2(NO3)2 (IV) with Co(II), Ni(II) and Cu(II) in the presence of nitrate or perchlorate anions. Despite similar syntheses, nitrate serves as a ligand to Cu(II) in IV whereas, it is seen as a free ion in the cell of Co(bptd)2(H2O)2(NO3)2 (I). Download : Download full-size image

New phases in the binary system PbO–BiVO4: Pb2BiVO6 and Pb4BiVO8

The binary system PbO–BiVO4 exhibits two new phases, Pb4BiVO8 and Pb2BiVO6. They both melt congruently at 780 °C. They have been identified by single-crystal and powder X-ray diffraction. Pb4BiVO8 crystallizes with a triclinic cell, a= 6.221(2)A, b= 7.603(5)A, c= 10.457(4)A, α= 100.40(3)°, β= 102.18(2)°, γ= 90.03(3)° and Z= 2. Pb2BiVO6 exhibits four phase transitions at 300, 415, 475 and 600 °C. The α phase, room-temperature form, is monoclinic with a=7.642(6)A, b= 5.81 2(5)A, c= 28.85(2)A, β=100.3(1)° and Z= 8. The β and γ phases are orthorhombic with a= 8.381(6)A, b= 16.65(1)A, c= 4.859(6)A, Z= 4 and a=14.304(7)A, b=10.14(1)A, c= 9.923(4)A, Z= 8, respectively. The δ phase is tetragonal with a= 12.110(2)A, c= 9.472(8)A and Z= 8.

A new family of compounds with tetrahedral anions: PbnBiOn(XO4), X = V, P, As, n = 1, 2, 4. A comparison with lead oxysulfates PbnPbOn(SO4)

Abstract The thermal behavior and crystallographic characteristics of nine compounds, PbnMOn(XO4) with M = Bi, Pb, X = V, P, As, S and n = 1, 2, 4, are reported. A previously reported γ phase for Pb2BiO2(VO4) was shown to consist of a mixture of PbBiO(VO4) and Pb4BiO4(VO4) that resulted from a kinetically controlled decomposition of Pb2BiO2(VO4) at elevated temperatures. The relationship between the α, β and δ transitions for Pb2BiO2(VO4) was clarified. All of these phases contain the tetrahedral anion XO4 that imparts thermal and structural similarities as well as specifications that can be ascribed to anion size differences.

The dependence of polymorphism on the ionic radius of Ln3+ (LnLaEr, Y) in the oxide ion conductors Bi0.775Ln0.225O1.5

Abstract This paper describes the polymorphic transitions of Bi0.775Ln0.225O1.5 (LnLaEr and Y), which is a representative composition of a rhombohedral solid solution over a limited range inside the 20–30 mol% Ln2O3. Three kinds of polymorphs are found: a hexagonal low-temperature modification (β2) isomorphous with Bi0.765Sr0.235O1.383 (BiSrO) type, a hexagonal intermediate (β1), and the well known high-temperature modification (δ) isomorphous with the fluorite type. The way the β2 phase behaves on heating can be divided into two groups depending on the Ln3+ ion: (1) one or two reversible transitions from β2 to β1, or from β2 to β1, then from β1 to δ for La, Pr, Nd, Sm, Eu and Gd; and (2) an irreversible transition from β2 to δ for the others. The thermal behaviour in group (1) closely resembles the BiSrO-type solid solution in the systems Bi2O3MO (MCa, Sr and Ba).

High temperature X-ray diffraction: An essential tool for phase diagram investigation. evidence of its role in the system Bi2O3-SrO

Abstract Previous descriptions of the Bi2O3-SrO system lead to significant discrepancies due to the use of different techniques. A new investigation, using high temperature X-ray diffraction unambiguously characterizes the different equilibrium phases as a fonction of the temperature. The most striking differences are: the presence of a fully reversible s2 - s1 phase transition in the rhombohedral domain; the thermal phenomenon observed at 780°C for the SrBi2O4 composition has to be associated to the decomposition into two solid solutions; the Sr6Bi2O9 compound is not part of the Bi2O3-SrO system but, due to a necessary stabilizing BiIII - BiV oxydation phenomenon, it must be formulated Sr6BiVyBiIII2−yO9+y with y > 0.

Synthesis and structure of some Co(III)-Bi(III) heterometallic complexes: [Co(NH3)5NCS][Bi(EDTA)]2.4H2O, trans-[Co(NH3)4(NO2)2][Bi(EDTA)(H2O)].2H2O, and [Co(NH3)4(CO3)][Bi(EDTA)].3H2O

Abstract Three Co(III)–Bi(III) heterometallic complexes: pentaammine-thiocyanato-cobalt(III) ethylenediaminetetraacetatobismuthate(III) dihydrate, [Co(NH3)5NCS](Bi(EDTA)]2·4H2O, (I), trans-tetraamminedinitrocobalt(III) ethylenediaminetetraacetato(aqua)bismuthate(III) dihydrate (trans-[Co(NH3)4(NO2)2][Bi(EDTA)(H2O)]·2H2O, (II), and tetraammine(carbonato)-cobalt(III) ethylenediaminetetraacetatobismuthate(III) trihydrate [Co(NH3)4(CO3)][Bi(EDTA)]·3H2O, (III) were synthesized and characterized by X-ray crystallography. Thermal decomposition of the complexes proceeds in several stages, dehydration, deamination, and finally pyrolysis of ligands leaving sillenite and traces of Co3O4 in the case of (II) and (III), and an unknown phase in the case of (I). Complex (II) is thus a potential precursor for Bi/Co mixtures in the ratio of 1/1.

Potassium-controlled synthesis of heterotopic macrocycles based on isothiosemicarbazide

The macrocyclisation reaction of 3,3′-(3,6-dioxaoctane-1,8-diyldioxy)-bis(2-hydroxybenzaldehyde) ( 1 ) with S -methylisothiosemicarbazide hydroiodide (H 2 NNC(SCH 3 )NH 2 ·HI) in the presence of potassium triflate, followed by addition of M(CH 3 COO) 2 · n H 2 O, where M=Ni, Cu, Zn, afforded [NiLKI 3 ] ( 2 ), [NiLK(CF 3 SO 3 )] ( 3 ), [CuLK(CF 3 SO 3 )(CH 3 OH)] ( 4 ) and [(ZnILK) 2 CH 3 OH] ( 5 ), respectively. Compounds 2 – 5 have been characterised by X-ray crystallography. IR, electronic, mass, 1 H, 13 C{ 1 H} and 19 F{ 1 H} NMR spectra are reported. Magnetic susceptibility measurements and ESR spectra of 4 indicate weak intermolecular spin–spin interactions, which are mostly dipolar in origin.

A new multiple perovskite family Sr3(Bi1−ySby)O5.5−δ(0≤y≤1)

Abstract The solid state reaction of an Sb 2 O 3 -SrCO 3 mixture (Sr/Sb=3/1) gives a mixed valency antinomy compound that can be written Sr 3 SbO 5.5−δ . Several structural modifications have been characterized by high temperature X-ray diffraction, TGA and DSC. The room temperature form is isostructural to (β)Sr 3 BiO 5.5 ; a transformation into a cubic 2ap×2ap×2ap superstructure is noted between 285 and 350°C. Over 350°C, the tetragonal pattern is isostructural to (α)Sr 3 BiO 5.5 , with a=8.460(2) A , c=16.493(6) A - both forms correspond to a maximum Sb v content. At 440°C the β form is again obtained. When annealed at 950°C, it yields a multiple perovskite superlattice. We have identified two solid solution domains Sr 3 (Bi 1− y Sb y )O 5.5− δ : for 0≤ y ≤0.25 the Sr 3 BiO 5.5 structural evolution versus temperature is kept and a cubic perovskite superlattice is stabilized for 0.3≤ y

The incommensurately modulated crystal structure of β‐Pb2BiVO6: interpretation of the phase transition α→β→δ and conduction properties of related materials

A new polymorph of Pb(2)BiVO(6) was prepared under ambient conditions and its crystal structure was determined by single-crystal X-ray diffraction. The phase transitions alpha --> beta and beta --> delta were identified in the mother phase; the high-temperature form delta-Pb(2)BiVO(6) eventually decomposes at 753 K to a mixture of Pb(4)BiVO(8) and the high-temperature form of PbBiVO(5) before showing recombination at 923 K. beta-Pb(2)BiVO(6) has an incommensurate monoclinic modulated structure. This crystal structure is twinned and complementary structural investigations of a powder sample of beta-Pb(2)BiVO(6) by TEM diffraction studies confirmed the lattice and incommensurate modulation character. Log sigma = f(T(-1)) dependences for Pb(2)BiVO(6)-related materials (6% M-for-V-substituted compositions; M = Cr, Mn, P) are reported, which allow the characterization (E(a) and isothermal sigma values) of the beta- as well as the delta- and alpha-Pb(2)BiVO(6) varieties.

Synthesis and microstructure of bismuth-based mixed metal oxides from organic precursors

Abstract A new method for synthesizing homogeneous oxide powders was studied. This paper reports the synthesis of organic precursors using 3,6-dicarboxypyridazine (DCP) as a precipitant. An important advantage of the method is its versatility due to the fact that DCP forms stable complexes for a wide range of elements. Thermogravimetric analysis was used to study the decomposition of the organic precursors and the reaction of the oxide products of pyrolysis.