A. Meerschaut

Preparation et structure cristalline de I0.33NbSe4(I4Nb12Se48)

Resume I0.33NbSe4, observe lors dessais de croissance cristalline de NbSe3 par transport sous iode, peut etre prepare par reaction directe entre les elements en proportions convenables a 700°C. La structure est determinee par diffraction des rayons X sur monocristal. La maille est quadratique avec a = 9.489 A, c = 19.13 A, le groupe spatial est p4 mnc avec Z = 12. Ledifice est constitue par un empilement dantiprismes a base rectangulaire [NbSe8]. Les atomes diode sont situes entre ces chaines.

Characterization of the new series of quasi one-dimensional compounds(MX4)nY (M =Nb, Ta; X =S, Se; Y =Br, I)

Abstract A detailed investigation on the new series of compounds(MX4)nY (M =Nb, Ta; X =S, Se; Y =Br, I)is given through structural information and resistivity measurements. All these compounds are built with the same framework which is composed ofMX4chains and halogen atoms between these chains. It is found that the resistivity behavior is closely related to the metal-metal sequence along theMX4chain.

The tailoring of crystal structures via the self-assembly of organic coordination compounds by N⋯I non-covalent halogen bonds: co-crystals of sterically hindered N-heterocycles and 1,4-diiodo-tetrafluorobenzene

The N-containing heteroaromatics 2,3,5,6-tetramethylpyrazine (tmpyr), 2,2′-bipyridine (2,2′-bpy), 2,4′-bipyridine (2,4′-bpy) and o-phenanthroline (phen) were each cocrystallized with 1,4-diiodo-tetrafluoro-benzene (TFDIB). The effect of the sterically constrained aza cycles on supramolecular assembly and the crystal structure determining interactions is discussed. The N⋯I non-covalent halogen bonds are the main directing interactions responsible for the observed structures. Nevertheless, steric hindrance of the donor sites increases the impact of weaker intermolecular interactions such as CH⋯F bonding and π–π interactions provoking changes in the coordination behaviour of the donor modules. In spite of steric constraints, the co-crystals tmpyr·TFDIB (1) and 2,2′-bpy·TFDIB (2) exhibit polymeric structures consisting of infinite one-dimensional chains of alternating electron donors (D) and acceptors (A). In contrast, the structures of the cocrystals 2,4′-bpy·TFDIB (3) and phen·TFDIB (4) reveal a packing of termolecular [A1D2] complexes. It follows that the structure type of such halogen bonded supramolecular assemblies can be tuned by choosing the appropriate precursors.

Structural determination of a new one-dimensional niobium chalcogenide : FeNb3Se10

Abstract FeNb 3 Se 10 is obtained by heating the elements at 650°C in silica evacuated tubes. The unit cell dimensions are : a = 9.213(1) A ; b= 3.482(1) A ; c = 10.292(1) A ; β = 114.46(4)° The structural determination on a single crystal shows the pseudo 1D-character of the compound. Two types of chains are running in the structure along the b axis. One of them corresponds to a trigonal prismatic frame of selenium, the other develops an octahedral distribution of selenium atoms. Iron is octahedrally coordinated whereas niobium presents both types of environment. The trigonal prismatic chains corresponds exactly to one of the conducting [NbSe 3 ] chains of niobium triselenide. FeNb 3 Se 10 is metallic at room temperature; it undergoes a metal-insulator transition below 140K.

Structure determination of a new misfit layer compound (PbS)1.18(TiS2)2

Abstract (PbS)1.18(TiS2)2 is a misfit layer compound in which two types of slabs, PbS and 2(TiS2), alternate along the c direction. The |TiS2| blocks (about 11.39 A thick) are interleaved by |PbS| layers, thus leading to a value for c of 17.46 A. The misfit between the two slab types occurs along the a direction; the parameter values being a( PbS )=5.761 A and a( TiS 2 )=3.390 A respectively. This yields a ratio of approximately 1.699, which is irrational but close to 5/3. The common in-plane b parameter is equal to 5.873 A. The PbS unit consists of a {001} slice (half an edge thick) of an NaCl-type f.c.c. cell.

Lead-antimony sulfosalts from Tuscany (Italy). IV. Crystal structure of pillaite, Pb9Sb10S23CIO0.5, an expanded monoclinic derivative of hexagonal Bi(Bi2S3)9I3, from the zinkenite group

The crystal structure of pillaite, a recently described Pb-Sb oxy-chloro-sulfosalt from the Buca della Vena mine, Tuscany (Italy), was solved and refined to a residual R of 0.045 in the monoclinic system, with space group C2/m, and a = 49.49(1), b = 4.1259(8), c = 21.828(4) A, β = 99.62(3) 0 , V = 4394(2) A3. The structural formula is Pb 9.16 Sb 9.84 S 23 ClO 0.5 , corresponding to the electron-microprobe one Cu 0.10 Pb 9.16 Sb 9.84 S 22.94 Cl 1.06 O 0.5 (ideally Pb 9 Sb 10 S 23 ClO 0.5 ), with Z = 4 and D cale. = 5.87. The crystal structure is organized around pseudo-threefold axes where chlorine atoms are in a trigonal prismatic coordination with Pb atoms. An oxygen position, half-filled, is bonded to two Sb atoms, like in scainiite. Pairs of pseudo-trigonal rods parallel to the elongation b-direction are connected along [102] to form rod-layers. The pillaite structure is an expanded homologue of hexagonal Bi(Bi 2 S 3 ) 9 I 3 . Among lead sulfosalts, it belongs to the zinkenite group of cyclically twinned structures. Pillaite is the first example of a Pb-Sb sulfosalt where small amounts of two anion species simultaneously play a specific crystal chemical role, which is essential for the stabilization of the crystal structure: chlorine, like in dadsonite, and oxygen, like in scainiite.

X-Ray structure determination and superconductivity of a new layered misfit compound with a franckeite-like stacking, [(Pb,Sb)S]2.28NbS2

Abstract The crystal structure of [(Pb,Sb)S]2.28NbS2 has been determined. This synthetic compound belongs to the layer misfit family with the structure type of franckeite. Its structure is built up from two [(Pb,Sb)S] layers (noted “Q”) alternating with one [NbS2] layer (noted “H”) along the stacking direction ( c axis). The cell parameters of this composite structure are: b = 5.8285(9) A , c = 17.649(6) A , α = 86.41(2)°, β = 86.55(3)°, γ = 89.97(2)° : Q sublattice a = 5.864(2) A : H sublattice a = 3.33 A . Antimony atoms are specifically located at the interface within the two “Q” layers as in natural franckeite. Stereochemical activity of Sb3+ (with its lone electron pair) stabilizes the double “Q” entity which has the SnS structure, giving the following structural formulation: [PbS (Pb0.6Sb0.4)S]1.14NbS2. A superconducting transition is observed at Tc = 1.05 K, a temperature lower than that observed for the corresponding 1Q/1H misfit derivative. This feature may be related to a decrease of the oxidation state for Nb, from +4 in the stoichiometric binary 2H-NbS2 compound (Tc = 6.2 K) to partially +3 in this compound. Crystal chemical constraints which govern the stabilization of franckeite-type compounds are discussed.

Lead-antimony sulfosalts from Tuscany (Italy). III. Pillaite, Pb9Sb10S23ClO0.5, a new Pb-Sb oxy-chloro-sulfosalt, from Buca della Vena mine

The new mineral pillaite, Pb9Sb10S23ClO0.5, an oxy-chloro-sulfosalt, has been found at Buca della Vena mine in the Apuan Alps, northern Tuscany, Italy. It crystallized in small fractures of dolomitic lenses in massive Fe- Ba ore, together with many Pb-Sb sulfosalts, among which the oxy-sulfosalt scainiite. Pillaite occurs as black acicu- lar crystals with metallic lustre, elongated // (010), up to 1 cm long and less than 0.1 mm thick. The mineral is brittle, opaque; VHN50 = 175 kg/mm2, dcalc = 5.77 g/cm3. In reflected light it shows a weak anisotropy and bireflectance, and

Lead-antimony sulfosalts from Tuscany (Italy). V. Definition and crystal structure of moëloite, Pb6Sb6S14(S3), a new mineral from the Ceragiola marble quarry

Moeloite is a new lead-antimony sulfosalt, Pb 6 Sb 6 S 14 (S 3 ), discovered in the Ceragiola marble quarry, near Seravezza town (Tuscany, Italy). Associated minerals are: sulphur, pyrite and enargite. It crystallizes as very thin needles and soft plumose aggregates of flexible thin fibres with a metallic lustre. Under the microscope it looks white, with moderate anisotropism, without polarization colours; reflectance values (air/oil): 40.0–37.8/26.6–24.2 (470 nm), 38.8–36.5/24.9–22.8 (546 nm), 38.6–36.7/23.4–21.4 (589 nm), 36.5–34.7/21.2–20.1 (650 nm). Moeloite is orthorhombic, space group P 2 1 22 1 , with unit cell parameters a 15.328(3), b 4.0400(8), c 23.054(5) A; V 1427.6(5) A 3 , with Z = 2; D calc. 5.86 g/cm 3 . Main X-ray powder diffraction lines [d(A), I, hkl ]: 3.724 (55)(106, 112), 3.427 (100) (403), 3.047 (85) (312, 214), 2.844 (58) (503), 2.779 (70) (016, 314), 2.753 (45) (116), 2.017 (80) (614, 020), 1.733 (50) (0112, 618, 2013). The crystal structure reveals Pb 6 Sb 6 S 16 rods parallel to b , and connected along c by a (S 3 ) 2- trimer due to an additional S atom, to form (100) rod-layers. The crystal structural formula is Pb 2+ 6 Sb 3+ 6 S 2- 14 (S 3 ) 2- . The formation of moeloite is subordinated to a high sulfur fugacity, which explains the S excess of its formula. The name is in honour of Dr. Y. Moelo (Nantes, France), who first synthesized this compound.

Lead-antimony sulfosalts from Tuscany (Italy). VI. Pellouxite, ∼ (Cu,Ag)2Pb21Sb23S55ClO, a new oxy-chloro-sulfosalt from Buca della Vena mine, Apuan Alps

Pellouxite, the second natural oxy-chloro-sulfosalt after pillaite, has been discovered in cavities of calcite veins in the small Fe-Ba deposit of Buca della Vena mine, Apuan Alps (Tuscany, Italy). The new mineral name honours professor Alberto Pelloux (1868–1948), curator of the mineralogical Museum at the University of Genova. Pellouxite occurs as black acicular flattened crystals with metallic lustre, up to 1 mm long and less than 0.05 mm thick. Main reflectance values [λ (nm), R air / R oil %]: 470, 38.3/23.8; 546, 37.3/22.4; 589, 36.9/21.5; 650, 35.2/19.6. It has monoclinic symmetry, space group C 2/ m , with a = 55.824(11), b = 4.0892(8), c = 24.128(5) A, β = 113.14(3)° and V = 5065(2) A 3 . The eight strongest lines of the X-ray powder diffraction pattern are [d(A), I obs (hkl)]: 4.002, 38 (606, 406); 3.878, 24 (206, 112); 3.562, 31 (804, 1202); 3.423, 100 (807, 1604, 407); 3.009, 25 (808, 912, 713); 2.948, 27 (1313, 1111); 2.265, 19 (409); 2.048, 20 (020). Electron probe microanalysis gives (mean of 15 spots; wt.%, error σ): Pb 47.17(20), Sb 31.16(23), Cu 0.89(5), Ag 0.59(5), S 19.08(6), Cl 0.33(3), O 0.39(15), Total 99.60. The unit formula, on the basis of Pb + Sb = 22 at. according to the crystal structure study, is (Cu 0.64 Ag 0.25 )Pb 10.36 Sb 11.64 S 27.07 Cl 0.42 O 1.11 ( Z = 4). Taking into account a 2 b superstructure, the crystal chemical formula is (Cu,Ag) 2-x Pb 21-x Sb 23+x S 55 ClO (x = 0.12; d calc. = 5.97 g/cm 3 ), derived from the stoichiometric one (Cu,Ag) 2 Pb 21 Sb 23 S 55 ClO. Pellouxite, structurally related to scainiite, is an expanded monoclinic derivative of synthetic hexagonal Ba 12 Bi 24 S 48 . It belongs to the zinkenite group of lead sulfosalts with cyclically twinned structures and their derivatives. Like for pillaite, its formation is the result of a complex sulfide deposition from hydrothermal brines, at relatively high temperature, and fO 2 /fS 2 conditions controlled by the pyrite-hematite-magnetite buffer.