Search

Fe[(CH3(CH2)2PO3)(H2O)] (1) and Fe[(CH3(CH2)17PO3)(H2O)] (2) were synthesized by reaction of FeCl2·6H2O and the relevant phosphonic acid in water in presence of urea and under inert atmosphere. The compounds were characterized by elemental and thermogravimetric analyses, UV–visible and IR spectroscopy. The crystal structure of (1) was determined from X-ray single crystal diffraction studies at room temperature: monoclinic symmetry, space group P21, a = 5.7 0 7 ( 1 ) A , b = 4.8 1 1 ( 1 ) A , c = 1 1.8 1 8 ( 2 ) A , and β = 9 8.6 2 ( 3 ) ° . The compound is lamellar and the structure is hybrid, made of alternating inorganic and organic layers along the c direction. The inorganic layers consist of Fe(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one from the water molecule, separated by bi-layers of propyl groups. A preliminary structure characterization of compound (2) suggests a similar layered structure, but with an interlayer spacing of 40.3 A. The magnetic properties of the compounds were both studied by a dc and ac SQUID magnetometer. Fe[(CH3(CH2)2PO3)(H2O)] (1) obeys the Curie–Weiss law at temperatures above 50 K ( C = 3.8 1 cm 3 K mol - 1 , θ = - 6 2 K ), indicating a Fe +II oxidation state, a high-spin d6 ( S = 2 ) electronic configuration and an antiferromagnetic exchange couplings between the near-neighbouring Fe(II) ions. Below T = 2 2 K , Fe[(CH3(CH2)2PO3)(H2O)] exhibits a weak ferromagnetism. The critical temperature of T N = 2 2 K has been determined by ac magnetic susceptibility measurements. Compound (2) shows the same paramagnetic behaviour of the iron (II) propyl derivative. The values of C and θ were found to be 3.8 cm 3 K mol - 1 and −44 K, respectively, thus suggesting the presence of Fe +II ion in the S = 2 spin state and antiferromagnetic interactions between Fe(II) ions at low temperatures. Zero-field and field cooled magnetic susceptibility vs. T plots do not overlap below T = 3 0 K , suggesting the presence of an ordered magnetic state. The critical temperature, T N , has been located by the peaks at T N = 2 6 K from the ac susceptibility (χ′and χ″) vs. T plots. Below T N hysteresis loops recorded in the temperature region 1 6 T 2 6 K show an S-shape, while below 15 K assume an ellipsoid form. They reveal that compound (2) is a weak ferromagnet. The critical temperature T N in these layered Fe(II) alkylphosphonates is independent of the distance between the inorganic layers.

La rouxelite, Cu 2 HgPb 2 2 Sb 2 8 S 6 4 (O,S)2, est une nouvelle espece de sulfosel decouverte dans le gisement a Fe-Ba de Buca della Vena (Alpes Apuanes, Italie). Elle se presente en cristaux aciculaires a eclat metallique dans des veines de calcite. Reflectance dans l'air (R%, λ en nm): 38.2 (470), 36.2 (546), 35.4 (589), 32.8 (650). La rouxelite est monoclinique, groupe d'espace C2/m, avec a 43.113, b 4.059, c 37.874 A, β 117.35°, V 5887 A 3 , Z = 2, D c a l c = 5.86 g/cm 3 . Les huit principales raies du diagramme de poudre en diffraction X [d en A(I)(hkl)] sont: 3.84(31)(10.0.8), 3.402(100)(10.0.2, 12.0.8, 115), 3.369(74)(714, 0.0.10), 2.815(70)(317, 11.1.4), 2.756(36)(516, 12.0.3), 2.251(31)(1.1.12, 3.1.11), 2.116(31)(11.1.15), 1.955(30)(19.1.5, 11.1.8). L'analyse a la microsonde electronique donne (% poids, resultat moyen de six analyses): Cu 1.34(5), Hg 1.76(9), Pb 45.08(15), Sb 31.50(14), S 20.07(11), O (struct.) 0.20, Total 99.95. La formule chimique, sur la base d'un total de 53 cations, est Cu 2 . 2 0 Hg 0 . 9 2 Pb 2 2 , 7 8 Sb 2 7 , 1 0 S 6 5 , 5 3 O 1 . 3 1 conduisant a la formule stœchiometrique equilibree Cu 2 HgPb 2 2 Sb 2 8 S 6 4 (O,S) 2 . L'etude aux rayons X sur monocristal, malgre une valeur mediocre de R (0.169), revele une structure tout a fait originale, avec Cu et Hg dans deux sites specifiques, tetraedrique pour Cu et octaedrique aplati pour Hg. Il y a egalement une position eclatee pour O,S, liee a deux atomes de Sb. Une majorite des atomes de Pb, Sb et S forment des colonnes organisees autour de pseudo-axes ternaires, derivees de Ba 1 2 Bi 2 4 S 4 8 hexagonal. La formule structurale est Cu 2 HgPb 2 2 . 6 Sb 2 7 . 4 S 6 4 . 6 7 O 1 . 3 3 . La structure resulte de la combinaison de deux types de rubans paralleles a b, en alternance suivant a, bordes par un feuillet-palissade parallele a (010). Cette architecture combinant trois modules donne une structure du type "boxwork", comme pour la neyite. Des domaines tres etendus equivalents sur le plan topologique sont egalement reconnaissables entre la rouxelite et la kobellite, qui ont environ 90% de leur motif structural en commun. La formation de la rouxelite parait subordonnee a la remobilisation et au depot hydrothermaux du mercure dans les Alpes Apuanes lors de la phase tectono-metamorphique apennine, a l'instar des gisements de mercure voisins de Ripa et Levigliani. Cette nouvelle espece est dediee au Professeur Jean Rouxel (1935-1998), chimiste du solide, fondateur de l'Institut des Materiaux a l'Universite de Nantes (France).

A second form of the literature-known layered weak ferromagnet Fe[(CH3PO3)(H2O)] has been isolated. The crystal structure determination of this new form (2) has been carried out at T = 300 , 200 and 130 K. It crystallizes in the orthorhombic space group Pmn21: a = 5.7177 ( 11 ) , b = 8.8093 ( 18 ) , c = 4.8154 ( 10 ) A , while form (1) crystallizes in the space group Pna21: a = 17.58 ( 2 ) , b = 4.814 ( 1 ) , c = 5.719 ( 1 ) A . Mossbauer spectroscopy on form (2) has been performed in the temperature range 4–300 K; and, at T ∼ 160 K , a drastic change in the quadrupole splitting (ΔE) and a broadening of the doublet components is noticed. But surprisingly, on cooling the crystal, no structural change is observed, which could account for the increase in Δ E . Below T = 25 K , 57Fe spectra transform into hyperfine splitting patterns which reveal a magnetically ordered state in agreement with the results of earlier magnetic susceptibility studies.

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.

Single crystal X-ray diffraction was used to determine the modulated structure of the misfit layer compound (LaS){sub 1.196}VS{sub 2}. This compound crystallizes in the triclinic system with cell parameters: a{sub s}=3.410 (1)A, b{sub s}=5.845(1)A, c{sub s}=11.191(2)A, {alpha}{approx}95.15(4), {beta}{approx}84.79(2) deg., and {gamma}{approx}89.98(2) deg., q=0.5978(4)a{sub s}*-0.002(1)b{sub s}*+0.004(2)c{sub s}*, and V{sub s}=221.2(1)A{sup 3}. A (3+1)D superspace group, X1-bar ({alpha},{beta},{gamma}), was used to analyze the complete structure (X is referring to a pseudo C centering). The largest modulation amplitudes are observed for La-S (between La (subsystem 2) and S (subsystem 1)), as well as V-V distances. In connection with the large V-V modulation, we observed the formation of 'linear vanadium clusters' that may impact on the transport properties.

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.

The crystal structure of pellouxite, a natural Pb-Sb-(Cu,Ag) oxy-chloro-sulfide from Tuscany (Italy), has been solved and refined using single-crystal X-ray-diffraction, with a final R = 0.044. The symmetry is monoclinic, space group C 2/ m , with a = 55.824(11), b = 4.0892(8), c = 24.128(5) A, β = 113.14(3)°, V = 5065(2) A 3 . The structural formula is close to (Cu 0.68 Ag 0.26 )Pb 10.44 Sb 11.56 S 27 (Cl 0.5 S 0.5 )O 0.5 , with Z = 4, or, ideally (according to ordering revealed by a weak 2b superstructure), (Cu,Ag) 2 Pb 21 Sb 23 S 55 ClO, with Z = 4. Among cations, there are 9 pure Pb positions, 10 pure Sb positions, and 3 Pb/Sb and one Cu/Ag pairs. Together with 27 S atoms, there are one Cl/S pair, as well as one isolated half-filled O position. All the minor elements (Cu with Ag, Cl and O) appear essential for the organization of the crystal structure. The Cu/Ag pair is located within a triangular bipyramid (four S and one Cl/S); vacancies on this site (fixed to 0.06 %) have been correlated to an equivalent Sb excess in the neighbouring Pb/Sb pair according to the substitution Pb 2+ + (Cu,Ag)+ → Sb 3+ + vacancy. The isolated oxygen is strongly bonded to two Sb atoms, like in scainiite and pillaite. The Cl/S pair is situated in a triangular prismatic coordination (4 Pb + 2 Sb). Following the principles of modular analysis, the whole structure is described in two ways: 1 - a combination of three types of 1 D and 2D building blocks, each of them organized around Sb 3+ lone-electron-pair micelles, or 2 - a single type of complex rod-layer parallel to (201), organized around columns with pseudo-trigonal symmetry. Pellouxite constitutes the second example of oxychloro-sulfosalt after pillaite. It is an expanded monoclinic derivative of synthetic hexagonal Ba 12 Bi 24 S 48 , structurally related to scainiite, Pb 14 Sb 30 S 54 O 5 (topological similarity for about 90 % of the atom positions). It belongs to the zinkenite group of cyclically twinned sulfosalt structures and derivatives.

A new phase in the quaternary system Gd/Ti/S/O was obtained from a mixture of Gd2O3, Gd2S3, TiO2, TiS2 and Ti by a solid state reaction at 1323 K in a sealed fused-silica tube. The structure of Gd6+xTi4−xS10−yO6+y (where x ~ 0.04, and y ~ 0.27), was solved by single-crystal X-ray diffraction, with R(obs) = 2.69% for 2391 reflections (I > 3σ (I)) and 155 variables. This compound crystallizes with four formula units in the orthorhombic space group Pnma, and the lattice constants (Å ): a = 13.991(1), b = 3.7124(2), c = 34.029(3) Å. The structure is built up from the stacking of ribbons of five Gd-polyhedra alternating with ribbons of five Ti- and Gd/Ti-polyhedra along the a-axis. This is the first example of a rare earth (RE) and titanium oxysulfide compound that shows mixed RE/Ti sites together with pure RE- and Ti-sites. Gd6+xTi4−xS10−yO6+y is a mixed-valent titanium oxysulfide in which half of the Ti cations are Ti3+ and half are Ti4+.

Two new compounds, La5Ti2MS5O7 (M=Cu, Ag) were synthesized and their structures solved from single crystal X-ray data. Both compounds are isotypic. They crystallize in the orthorhombic system (space group Pnma, Z=4) with lattice constants a=19.423(1) A, b=3.9793(2) A, c=18.1191(9) A for La5Ti2CuS5O7, and a=19.593(2) A, b=3.9963(1) A, and c=18.2973(15) A for La5Ti2AgS5O7. The structure of these compounds is built from fragments of the rock-salt, perovskite and fluorite types and a clear anionic segregation of the anions appears in the structure. La5Ti2CuS5O7 and La5Ti2AgS5O7 exhibit an orange-yellow color and measurement of their optical band gap gave 2.02 and 2.17 eV, respectively.

A new phase Sm2Ti2S2O4.5 was synthesized and its crystal structure was solved by single-crystal X-ray diffraction. This compound crystallizes in the monoclinic system (C2/m) with lattice constants a=17.9987(11) A, b=3.71607(14) A, c=12.6172(8) A and β=133.645(4)°. The structure is built up from double chains of Ti-centered octahedra between which Sm-polyhedra develop. In spite of very close formulations, the structure of Sm2Ti2S2O4.5 differs completely from that of the defect Ruddelsden–Popper phase Sm2Ti2S2O5 previously reported. The title compound presents a mixed valence for titanium with Ti(III) (d1) and Ti(IV) (d0) located in different crystallographic sites. However, conductivity measurements show that this compound is non-metallic.

Two new compounds, LaInS 2 O and La 5 In 3 S 9 O 3 were synthesized in the La–In–S–O quaternary system. Both compounds crystallize in the orthorhombic system with lattice constants a =20.5421(6) A, b =14.8490(4) A, c =3.9829(1) A for LaInS 2 O, and a =4.1018(1) A, b =26.833(1) A, c =16.023(1) A for La 5 In 3 S 9 O 3 . The structure of La 5 In 3 S 9 O 3 was solved from single-crystal X-ray data, in the space group Pbcm , with Z =4; it is built from three-atom-thick (100) NaCl layers interleaved with fluorite-type ribbons, and is closely related to the structures of the known lanthanum and indium compounds La 10 In 6 S 17 O 6 and La 4 In 5 S 13 . Both compounds LaInS 2 O and La 5 In 3 S 9 O 3 exhibit a yellow color; measurement of their optical gaps gave 2.73 and 2.60 eV, respectively.

The tetra-imino ferrocenophane (1) was cocrystallized with 1,4-diiodo-tetrafluoro-benzene (TFDIB). In the resulting compound 2, two of the four ferrocenophane nitrogens show interactions with the iodine atoms of TFDIB leading to a polymeric structure with extended linear alternating electron donor (1) and acceptor (TFDIB) molecule chains. For the first time, imino nitrogens are involved in this type of halogen bonding. The N⋯I non-covalent bonds (N⋯I distances 2.879(5) and 2.896(5) A; N⋯I–C angles 171.1(2) and 178.1(2)°) are the directing interactions responsible for the observed self-assembly. The ferrocene fragments of the macrocycle are in an almost perpendicular conformation. Mossbauer spectroscopy indicates the sole presence of low spin iron (II). The temperature dependence of the magnetic susceptibility is corresponding to a quasi-diamagnetic compound.

The [Sr(Fe0.77Nb0.23)0.5S1.5]1.13NbS2 phase belongs to the 2D-misfit compounds family which are formed of two kinds of slabs labeled Q and H. The Q-part is a three-layer-thick slab, with the NaCl type structure, where external SrS planes enclose the inner (Fe,Nb)S plane. In a previous paper it was shown that there is a statistical distribution of the iron and sulfur atoms in the central layer of the Q-part. On the other hand, niobium atoms adopt an octahedral environment. To get a better description of this central layer, X-ray absorption and HREM studies were undertaken. EXAFS measurements clearly show that the environment of Fe atoms is less complex than that suggested from the structural determination. The existence of only one value for the Fe−S distance confirms the presence of [FeS4] tetrahedra as previously shown by the Mossbauer study. Both [NbS6] and [FeS4] polyhedra can arrange themselves in clusters. Electron diffraction and HREM studies reveal two new additional periodicities which can origina...

A new misfit layer compound (EuS)1.173NbS2 was synthesized, and its structure was solved in a (3+1)D superspace using the superspace group Xm2m(α00) with X referring to a pseudo F centering. The ce...

Crystal structures of two new misfit compounds, [SrGd 0.5 S 1.5 ] 1.16 NbS 2 and [Sr(Fe,Nb) 0.5 S 1.5 ] 1.13 NbS 2 , were determined through the composite approach, i.e., by refining each subpart ( Q , H -parts, and the common part) of these composite materials, separately. The Q -part is a three-atom-thick layer, with the NaCl-type structure, where external SrS planes enclose the inner GdS or (Fe,Nb)S plane; the structural difference between these two compounds lies in the central layer within the Q -part: Gd and S atoms are in special positions (octahedral coordination), while Fe and S atoms are statistically distributed on split (×4) positions (tetrahedral coordination) around a central unique site (=special position occupied by Nb). The H -part is a sandwich of sulfur planes enclosing the inner Nb plane as observed for the structure of the binary compound NbS 2 itself. The Sr–Gd derivative shows a paramagnetic behavior in the whole studied temperature range (2–300 K). On the other hand, antiferromagnetic interactions occur in the Sr–Fe derivative; the complex magnetic behavior of this compound is related to the statistical distribution of Fe atoms which leads to frustration of the magnetic interactions. At room temperature, experimental values obtained from Mossbauer spectrum correspond to Fe 3+ in tetrahedral sulfur environment: isomer shift δ=0.32 mm s −1 , and quadrupole splitting Δ E =0.48 mm s −1 .

The crystal structure determination of two new oxychalcogenides, namely Eu 5 V 3 S 6 O 7 and La 10 Se 14 O, is reported. Eu 5 V 3 S 6 O 7 crystallizes in the orthorhombic symmetry (space group Pmmn ) with unit cell parameters (in A): a =17.463(2), b =3.6732(4), and c =10.007(1). This compound is isotypic with the Ln 5 V 3 S 6 O 7 compounds (Ln=La–Nd), and its structure has been refined to R 1=0.0248. Eu atoms, which are nine-coordinated by O and S atoms, are associated to form ribbons that are interconnected by [VS 4 O 2 ] octahedrons. La 10 Se 14 O crystallizes in the tetragonal symmetry (space group I 4 1 / acd ) with unit cell parameters (in A): a =15.926(2), and c =21.061(5). The structure was refined to R 1=0.0347. La 10 Se 14 O is isostructural with the Pr 10 X 14 O compounds (X=S and Se). The only structure difference is observed for one La site that is found split, in connection with a mixed O/Se site filling.

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.

A new series of compounds, Ln2Ti2S2O5 with Ln from Pr to Er, has been recently reported. These compounds crystallize in the tetragonal I4/mmm space group, with a≈3.8 A and c≈22.9 A. Their 3D-structure can be schematically described as a 2D-stacking of [Ln2S2] layers alternating with [Ti2O5] ones, both layers being connected through Ln–O (×4) and Ti–S (×1) bonding. Magnetic measurements using a SQUID magnetometer indicate paramagnetic behavior over a large temperature range, obeying a Curie–Weiss law (at least between 90 and 300 K), for all the studied lanthanides. An antiferromagnetic transition at TN k → i (kx,0,0); kx≈0.46, to a commensurate state with a change in the direction of k → c (1/2,0,1/2) when the temperature is lowered (T

The optical properties of Ln 2 Ti 2 S 2 O 5 compounds ( Ln =Nd, Sm, Gd, Tb, Dy, Ho, Er, and Y) have been measured. Diffuse reflectance spectra revealed a strong absorption band above 2 eV, which explains the color of the compounds. Moreover, other bands, with a lower intensity, have been attributed to 4 f –4 f rare earth transitions. In the case of neodymium the derived energy level scheme is rich enough to determinate a set of phenomenological crystal field parameters that correctly reproduce the spectrum. These parameters were also calculated from the crystallographic structure, in a good agreement with the experiment. Finally, the paramagnetic susceptibility, well reproduced by the calculation, confirms that the rare earth is in a trivalent state.

Cu-poor meneghinite from La Lauziere Massif (Savoy, France) has the composition (electron microprobe) (in wt%): Pb 59.50, Sb 20.33, Bi 1.19, Cu 0.87, Ag 0.05, Fe 0.03, S 17.62, Se 0.05, Total 99.64. Its crystal structure (X-ray on a single crystal) was solved with R 1=0.0506, wR 2=0.1026, with an orthorhombic symmetry, space group Pnma , and a =24.080(5) A, b =4.1276(8) A, c =11.369(2) A, V =1130.0(4) A 3 , Z =4. Relatively to the model of Euler and Hellner (1960), this structure shows a significantly lower site occupancy factor for the tetrahedral Cu site (0.146 against 0.25). Among the five other metallic sites, Bi appears in the one with predominant Sb. Developed structural formula: Cu 0.15 Pb 2 (Pb 0.53 Sb 0.47 )(Pb 0.46 Sb 0.54 )(Sb 0.75 Pb 0.19 Bi 0.06 )S 6 ; the reduced one: Cu 0.58 Pb 12.72 (Sb 7.04 Bi 0.24 )S 24 . The formation of such a Cu-poor variety seems to be related to specific paragenetic conditions (absence of coexisting galena), or to crystallochemical constraints (minor Bi). To cite this article: Y. Moelo et al., C. R. Geoscience 334 (2002) 529–536.

A new compound Gd 4 TiSe 4 O 4 has been obtained by a solid state reaction of Gd 2 O 3 , TiO 2 , and TiSe 2 , at T =1000°C, with the addition of iodine to favor crystallization. Single-crystal X-ray diffraction measurements show that Gd 4 TiSe 4 O 4 crystallizes in space group C 2/ m (No. 12) of the monoclinic system with two formula units in a cell of dimensions a =15.7878(4) A, b =3.7610(2) A, c =9.6639(3) A, and β =117.569(2)°. The structure contains two crystallographically independent Gd atoms with a bicapped trigonal prismatic coordination. Association of four adjacent Gd-centered polyhedra constitutes the elemental building unit, which develops into ribbons along b . The ribbons are interconnected by infinite chains of edge-sharing Ti-centered octahedra. Magnetic susceptibility of the title compound has been measured from 1.8 to 300 K, and from B =1.10 −3 to 0.1 T for the ZFC and FC cooling modes. The linear variation of the inverse susceptibility versus T can be modeled with a Curie–Weiss law in agreement with a Gd 3+ free ion behavior. The maximum of the χ (T) curve at about 2.5 K could be attributed to both an antiferromagnetic transition and the saturation of the weak ferromagnetic component.

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.

Crystal structure determinations of two niobium dichalcogenides (3R- Nb1.09S2 and 2H-NbSe2) are reported: the sulfide compound that crystallizes in the R3m space group (a = 3.3297(6) A, c = 17.869(5) A) has been refined to a RF value of 2.63%, while the selenide compound crystallizing in the P63/mmc space group (a = 3.4425 (5) A, c = 12.547 (3) A) has been refined to a RF value of 1.33%. The sulfide derivative is nonstoichiometric with extra Nb atoms statistically distributed over the vacant octahedral sites [site occupancy factor (s.o.f.) ≈ 9%] within the van der Waals gap separating two adjacent NbS2 sandwiches (where Nb is in a trigonal prismatic coordination). On the contrary, the selenide derivative appears perfectly stoichiometric.

We present magnetic properties of the recently reported 2D-misfit layer compounds [((Pb,M)S) 1.5 ] 1+ x NbS 2 for M=Fe or (Mn,Nb). For both the title compounds, the antiferromagnetic interactions are strong. Consequently, the linear variation of the inverse magnetic susceptibilities versus temperature cannot be interpreted by a Curie–Weiss law ( χ = C /( T – θ )) in the investigated temperature range. In the iron compound, an antiferromagnetic transition is observed at 25 K with a large magnetic hysteresis between the zero field cooled and field cooled susceptibilities. Magnetic frustration could explain this anomalously low transition temperature. The antiferromagnetic interactions in the manganese compound are smaller, as no transition is observed down to 2 K.

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

The new compound Sm3Ti3Se2O8 has been synthesized by a solid state reaction of Sm2O3, TiO2, and TiSe2 at T=1000 °C. This compound crystallizes in the monoclinic symmetry, space group P21/m (No. 11), with unit cell parameters: a=9.7844(6), b=3.8865(5), c=13.330(1) A, and β=111.37(1)°, Z=2. Its crystal structure can be roughly described as small fragments [SmSe] of a rock-salt-type structure interconnected by a complex entity built up from the condensation of edge sharing [TiO] octahedra. Refinement for 1019 independent reflections and 73 variables converged to the reliability factor RF=2.00 % (for 942 reflections satisfying the criterion I≥3σ(I)). Magnetic susceptibility of the title compound has been measured from 2 to 300 K and has shown a paramagnetic behavior of the van Vleck Sm3+ cation in the whole temperature range.

The new layered misfit sulfide of the 1.5Q/1H homologue type, (Pb(Mn, Nb)0.5S1.5)1.15NbS2, has been synthesized. Electron probe microanalysis gives the chemical formula (Pb1.02Mn0.33Nb0.16 S1.50)1.15 NbS2, indicating Nb incorporation in the rock-salt-type part (Q layer). Its crystal structure has been solved through a superspace approach: orthorhombic symmetry, superspace group Cm2m(α00), cell parameters a=3.326(1), b=5.788(1), c=14.326(3) A, q vector (0.5744(2),0,0); R=2.27% for 688 reflections and 36 variables. Nb-for-Mn substitution in the central part of the Q layer is clearly proved. Bond valence calculation on this compound, compared to some other misfit compounds, makes it possible to evaluate the charge transfer that governs the stability of such composite materials. This calculation, which takes into account the modulation of Pb–SH bondings at the Q/H interface through the superspace approach, shows that the transfer depends on the nature of cations in the Q layer. This leads to a formal oxidation state for Nb, within the H layer, varying between ∼3 and 3.6.

The crystal structure of scainiite, Pb 14 Sb 30 S 54 O 5 , has been solved from single-crystal X-ray data and refined to an R index of 8.9 % based on 3703 unique reflections. The structure is monoclinic C 2/ m , with cell parameters a 51.996(8), b 8.148(1), c 24.311(4) A, β 104.09(1)°, V 9990(10) A 3 , and with Z = 4. The structure analysis was essential in determining the position of oxygen atoms in a special double-ribbon, Sb 8 (Pb,Sb) 2 S 10 O 5 , directly related to the structure of kermesite, Sb 2 S 2 O. The general organization of the structure can be described according to the general principles developed by Makovicky (1993) for complex sulfides related to the PbS and SnS archetypes. This structure falls into the group of “pure rod structures” (zinkenite group), and is an expanded homologue of cyclic hexagonal Ba 12 Bi 24 S 48 . The expansion of the parent structure is obtained by shearing along a zig-zag surface, that creates lozenge shaped spaces in place of the original hexagonal channels, and filling these spaces by the kermesite-type fragments.

La ∼10.8 Nb 5 O 20 S 10 was obtained in an attempt to prepare the La homologue of the Sm 3 NbO 4 X 3 derivatives ( X =S, Se). Its structure was solved by X-ray diffraction on a single crystal, in the Immm space group with cell parameters a =32.535(8) A, b =12.115(3) A, and c =3.9999(3) A. Refinement of 58 parameters using 836 unique reflections with I >2 σ ( I ) converged to R 1 =5.09% and w R 2 =10.87%. The structure of La ∼10.8 Nb 5 O 20 S 10 can be schematically described as the stacking of [La 2 S 2 ] slabs of rock salt type (two-atom-thick layers) pillared by an intricate assembly of La and Nb polyhedra along the a -direction. Within this complex part, one of the La sites (La5) is partially occupied.

The new compound Sm 3 NbO 4 S 3 was obtained and its structure was determined by single crystal X-ray diffraction. The following crystal data were obtained: M r = 704.14 g·mol −1 , orthorhombic symmetry with unit cell parameters a = 6.6890(13), b = 7.6630(15), and c = 14.216(3) A, space group Pn 2 1 a (No. 33). Refinement from 2447 unique reflections with I > 2σ (I), and 101 variables, converged to the reliability factor R = 2.46%. Two different types of polyhedra can be distinguished: a bicapped trigonal prism around Sm2 and Sm22, and a very distorted prism with eight surrounding atoms (four O and four S atoms) around Sm1 and Nb1.

The structure of the new compound Nd 16 Ti 5 S 17 O 17 was determined by single-crystal X-ray diffraction. The following data were obtained: M r =3364.4 gmol −1 , tetragonal symmetry, space group I 4/ m (No. 87), unit cell parameters a =22.153(2) A, c =3.9426(3) A, V =1935 A 3 , Z =2. Refinement for 1282 unique reflections and 62 parameters converged to the reliability factor R =2.22% (for 1059 reflections with I ≥3 σ ( I )). The structure can be schematically described on the basis of [NdS] plane fragments connected by “(Nd 8 S 9 )” clusters, which delimit a filled channel of squared section. Within these channels, octahedral Ti-centered chains are developed along the c axis.

Stability of misfit layer chalcogenides (M.L.C.) is always governed by a charge transfer (C.T.) mechanism. A comparison between M.L.C. and parent intercalated layered binary systems shows comparabl...

Recent studies of the electronic structure of the rare earth misfit layer compounds (LnS)1 + xTS2 (Ln = rare earth, T = Ti, V, Cr, Nb, Ta) allow one to present a model which explains their stability. Two redox competitions, one between the [LnS] and the [TS2] slabs, and the second between the T nd and S 3p bands, are found to govern the stabilization of these compounds. This study shows how the modification of the electronic structure of each slab, by moving along the rare earth or the transition elements, defines a narrow stability range for the misfit layer structure.

The complete structure of the misfit layer compound [(EuS) 1.5 ] 1.15 NbS 2 is described as a (3+1)-dimensional intergrowth compound with two modulated subsystems ( ν =1, 2, for NbS 2 and EuS, respectively) which have the (a * ν 2 , a * ν 3 ) reciprocal-lattice plane in common. A superspace embedding follows from four reciprocal-lattice vectors given by a * 1 =a * 11 , a * 2 =a * 12 , a * 3 =a * 23 , and a * 4 =a * 21 . The symmetry is given by the superspace group G s = Fm 2 m ( α 00) with modulation wave vector q=a * 21 = α a * 11 ( α =0.5768(1)). The structure of this composite compound is built up of an alternated sequence of two different types of slabs (i.e., NbS 2 ( H -part) and EuS ( Q -part)), stacked along the c direction. The Q -part is a three-atom-thick layer (Eu2S2-Eu1S1-Eu2S2). The NbS 2 subsystem has cell parameters a 11 =3.3241(4) A, a 12 =5.7841(5) A, and a 13 =14.816(2) A, with space group Cm 2 m . The EuS subsystem has lattice parameters a 21 =5.7628(5) A, a 22 =5.7841(5) A, and a 23 =29.632(4) A, with space group Fm 2 m . Refinements on 1721 unique reflections converged to R =3.58% ( R w =4.75%) on a modulated structure model with 50 parameters. The largest modulation amplitudes occur on the outer Eu2 atoms. A bond-valence calculation using results from this structure determination shows that Eu atoms on the exterior sides (Eu2) of the EuS slab are in the +II oxidation state while inner Eu atoms (Eu1) are at the +III state. Mossbauer and magnetic measurements confirm the mixed-valence (Eu 2+ /Eu 3+ ) state of this compound. A ferromagnetic long-range order appears below 7 K.

We investigate the transport and magnetic properties of 2D (LaS) 1.18 VS 2 misfit compound single crystals. While the conductivity is characteristic of a hopping system with localized charge carriers, the magnetic susceptibility exhibits a clear signature of a low dimensional metal. We suggest that these paradoxal observations can be reconciled by taking into account the underlying 1D character of the t 2 g -t 2 g interactions within the VS 2 plans and the strong anisotropic displacive modulation on the V site. This suggestion is supported by band structure calculations.

Dilution of the magnetic interactions between Cr 3+ ions by Ti 3+ ions was observed in the CrS 2 layer of the misfit-layer compound ∼LaCrS 3 . Pure ∼LaCrS 3 has complex magnetic properties which are reminiscent of spin glass behavior. This magnetic behavior comes from both the modulated character of the structure and the magnetic frustration of the planar-antiferromagnetic-triangular network of Cr 3+ ions. Thus, there is a large hysteresis between the zero field cooled and the field cooled magnetic susceptibility curves below the transition temperature (≈75 K). Formation of a solid solution ∼LaCr 1− x Ti x S 3 by the addition of Ti 3+ ions results in the decrease of transition temperature up to a doping level of x ≈0.5, where the transition is no longer observed. The magnetic behavior of the phase with x ≈0.5 is similar to that of several random exchange antiferromagnetic compounds.

A crystal structure study of the layered misfit compound (Pb 2 FeS 3 ) 0.58 NbS 2 has been performed using the composite approach. The structure can be described on the basis of a regular alternation of [Pb 2 FeS 3 ] and [NbS 2 ] slabs stacked along the c direction. The [Pb 2 FeS 3 ] part has a thickness of three layers, the central ∣FeS∣ layer being sandwiched between the two external ∣PbS∣ layers. Thus, Pb atoms on the exterior sides of this part are in a squared-pyramidal sulfur coordination, while Fe atoms in the central zone are octahedrally and tetrahedrally surrounded by sulfur atoms. From bond valence calculations, Fe atoms are found in the +III oxidation state whatever their environment. This is corroborated by a Mossbauer study. Magnetic and electrical properties complete this study.

Sm 2 Ti 2 O 5 S 2 was obtained in an attempt to prepare an oxysulfide of samarium and titanium in a way similar to the obtention of the quaternary Sm 3 NbO 4 Se 3 compound. The structure was determined by single-crystal X-ray diffraction. The following crystal data were obtained: M r = 540.6 g mol −1 , tetragonal symmetry with unit cell parameters a = 3.819(1) A, c = 22.964(5) A, space group I4/ mmm (139). Refinement for 127 unique reflections with I > 3σ(1), and 11 variables, converged to the reliability factor R = 1.77 %. The structure can be described as a stacking, along the c -direction, of [Sm 2 S 2 ] slabs of a rock-salt type (two-atom-thick-layers) separated by a 2D network of corner-sharing octahedra [= Ti 2 O 5 ] of a ReO 3 structure type.

LnCrS{sub 3} (Ln = La, Ce, Nd, Sm) with NH{sub 4}CdCl{sub 3} structure type were prepared in high pressure synthesis at 4 GPa, 1,373 K for 2 h. Their orthorhombic lattice parameters were a = 0.787(2), b = 0.385(1), c = 1.334(3) nm for LaCrS{sub 3}; a = 0.776(4), b = 0.379(2), c = 1.316(7) nm for CeCrS{sub 3}; a = 0.769(2), b = 0.3771(1), c = 1.306(4) nm for NdCrS{sub 3}; and a = 0.764(5), b = 0.374(2), c = 1.297(8) nm for SmCrS{sub 3}. The Ln{sup 3+} ions are coordinated with nine S{sup 2{minus}} ions in CrS{sub 6} double chains. The products are antiferromagnetic semiconductors. The paramagnetic temperature {Theta} varied with a Cr-Cr distance in the CrS{sub 6} double chain. They also showed a weak ferromagnetic behavior at low temperature below 120 K. Magnetic hysteresis was observed for the ferromagnetism between ZFC and FC measurements. LaCr{sub 1{minus}x}Fe{sub x}S{sub 3} solid solution with NH{sub 4}CdCl{sub 3} structure type was also obtained in high pressure synthesis at 4 GPa, 1,473 K for 2 h. The Fe{sup 3+} in high spin state substitutes the Cr{sup 3+} up to about x = 0.2.

A new oxychlorosulfide compound La 5 Ti 6 S 3 Cl 3 O 15 has been prepared from the reaction of LaOCl with a mixture of La 2 S 3 and TiS 2 . Single crystal X-ray diffraction studies show that this compound crystallizes in the space group Im -3 (# 204) of the cubic system ( a =12.4156(6) A, Z =4). Data collection was obtained using a CAD4 Enraf Nonius diffractometer. Structural refinement was made with the program SHELXTL using 783 independent reflections. The final refinement resulted in conventional R factors, R 1 =0.038 for 563 reflections, with F>4 σ (F), R =0.069, and R w (F 2 )=0.126 for all reflections. The structure contains two types of La atoms with coordinations of 10 and 12, and Ti is in a distorted octahedral coordination to five oxygen atoms and one sulfur or chlorine atom.

New compounds La M S 3 with NH 4 CdCl 3 -type crystal structure could be prepared by high-pressure synthesis where M =Ti, V, Cr. The high-pressure compounds were obtained above 2.5 GPa at 1375 K for M =Cr, above 3.5 GPa at 1375 K for M =Ti, and above 5 GPa at 1475 K for M =V, respectively. The crystal structure of LaCrS 3 was refined as NH 4 CdCl 3 -type structure. It has an orthorhombic crystal lattice ( Pnma ) with a =0.787(1), b =0.3851(7), and c =1.334(2) nm. The polycrystalline product of LaCrS 3 was semiconducting and antiferromagnetic with T N =195 K and μ eff =3.83 μ B .

The crystal structure of the new misfit compound [(EuS)1.5]1.15NbS2 has been determined via the composite approach. The structure is built up from three [EuS] layers (= slab noted ‘Q’) alternating with the [NbS2] sandwich (= slab noted ‘H’) along the stacking direction (c axis). The cell parameters (A) of this composite structure are: Q-part, a = 5.760(1), b = 5.780(1), c = 29.734(5); H-part, a = 3.317(1), b = 5.790(1), c = 14.859(4). Eu atoms located on the exterior sides of the Q-part show a quite regular hemi-octahedral coordination, whilst the inner Eu atoms show a distorted octahedral coordination. From bond valence calculations, one can assume that the outer Eu atoms are at the +II oxidation state and the inner Eu atoms at the +III state. The structure of the H-part appears very comparable to that found for other misfit compounds, i.e., Nb atoms in a trigonal prismatic coordination with S atoms, as for the binary NbS2 itself.

Sm 3 NbSe 3 O 4 has been synthesized and its structure determined. The following crystal data were obtained: M r =844.84 g·mol −1 , orthorhombic, Pnma , a =6.8943(4) A, b =7.7529(8) A, c =14.7644(12) A, V =789.2(1) A 3 , Z =4, D x =7.111 g·cm −3 , Mo Kα , λ =0.71073 A, μ =372 cm −1 , F (000)=1444, T =295 K, R =0.035 for 1466 unique reflections with F o >4 σ ( F o ), 62 variables, GoF=0.818. The structure of Sm 3 NbSe 3 O 4 was determined by single-crystal X-ray diffraction. Two distinct types of polyhedra can be distinguished: a very distorted one with eight surrounding atoms (four O and four Se atoms) around Sm1 and Nb, and a bicapped trigonal prismatic one around Sm2. The crystal structure of this new compound can be described on the basis of corrugated planes perpendicular to the c axis. These planes are built up from edge-sharing trigonal prismatic polyhedra (Sm2); connection between successive planes is achieved through the distorted polyhedra which surround atoms Sm1 and Nb.

The structure of the new compound Eu27T20X2S54O12 (X ≈ I0.35 Cl0.65), prepared by solid state reaction, contains ∞2[(Ti4S2O4)(Ti2S10)4/2] planes built up from rutile-like chains that cross perpendicularly. Two [TiS6] octahedra separate the [Ti4S2O4] clusters at the chain intersections. These planes are separated by a corrugated layer of [Ti3S8O4] triplets of face-sharing Ti-centered octahedra. Five crystallographically independent europium ions are seven- to nine-coordinated.

The new compound La8Ti10S24O4has been prepared from a mixture of La2Ti2O7and La2O3(in a 5:1 ratio) heated at 1200°C under a H2S gas flow. This new quaternary phase was obtained due to an incomplete sulfidizing process. Single-crystal X-ray diffraction studies show that La8Ti10S24O4crystallizes in space groupP4/mmm, withZ=1, in a cell of dimensionsa=b=10.421 A andc=8.384 A. Least-squares refinement converged to values ofR=0.045 andRw=0.048. The structure can be viewed as a stacking of two types of layers along the c → axis. These layers are built up from infinite rutile-like chains (Ti octahedra) that cross perpendicularly. La atoms, in a tricapped prismatic coordination, are located in tunnels that develop parallel to the c → direction.

The new compound Ce20Ti11S44O6 crystallizes in space group D2h13-Pmmn of the orthorhombic system with two formula units in a cell of dimensions a = 22.4628(8), b = 14.2531(7), and c = 10.382(2) (T= 293 K). Isostructural with La20Ti11S44O6, this compound comprises ∞2[(Ti4S2O4(TiS6) 2 2 (Ti2S10) 2 2 ] layers of [Ti4S2O4] clusters linked together by edge-sharing, rutile-like chains of TiS6 octahedra. An additional pair of corner-sharing, oxygen-bridged, Ti-centered octahedra are found separated from the covalently-bonded layers. Charge balance restrictions require that Ti atoms be in the mixed oxidation states of 3+ or 4+. The seven crystallographically independent Ce atoms are found in three different coordination polyhedra.

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.

Resume Un nouveau chalcogenure lamellaire de la famille des structures composites incommensurables a ete obtenu dans le systeme Pb-Fe-Nb-S. Sa caracterisation preliminaire (analyse a la microsonde electronique, diffraction X, microscopie electronique) est presentee. Ce compose correspond a un nouveau type d'homologue ou alternent un feuillet NbS2 pseudo-hexagonal (H) et un feuillet a triple couche atomique ~ Pb2FeS3 pseudo-quadratique (Q) (homologue 1,5Q/1H). Les parametres cristallins sont (A): aQ = 5,773(1), aH= 3,3461(7), bQ = bH = 5,803( 1 ), cQ = cH = 14,106(2), α = β = γ = 90 °. Le fer est localise dans la couche centrale du feuillet Q, ce qui donne la formule chimique simplifiee (Pb2FeS3)0,58NbS2. Le fer joue un role cristallochimique specifique permettant la stabilisation de cette phase, tout comme l'antimoine dans les homologues 2Q/1H du type franckeite. Le mode de structuration du feuillet Q se retrouve dans d'autres chalcogenures et oxychalcogenures.

The structure of Sm2/3Cr2S4has been solved from single-crystal X-ray diffraction data. This compound presents a 3 ×asuperstructure alongaand an incommensurate superstructure alongbclose to 3 ×b. The basic structure is described in the space groupPmnbwitha= 3.5030(3) A,b= 10.9199(8) A,c= 12.7987(8) A,Z= 4,R= 0.046 for 916 observed reflections. The modulated structure refinement, taking into account the two superstructures, was carried out in a (3 + 2)D superspace group and leads toR= 0.063 for 1706 reflections. This structure consists of staggered double columns of [CrS6] octahedra connected by samarium atoms in a trigonal prismatic bicapped environment. This structure is reminiscent of that found in the lillianite mineral family. The statistical occupancy of samarium atoms (1/3), in agreement with the charge equilibrium (Sm3+, Cr3+, S2−), is related to the superstructure.

The composite bilayer misfit compound (SmS) 1.25 (TiS 2 ) 2 was prepared and its structure determined via the composite approach by single crystal X-ray diffraction. This compound crystallizes with monoclinic unit cells (SmS subcell: a 1 = 5.473(4) A, b 1 = 5.854(2) A, c 1 = 33.53(1) A, α 1 = 93.36(5) °, β 1 = 90 °, γ 1 =90 °; TiS 2 subcell a 2 = 3.425(3) A, b 2 = 5.854(2) A, c 2 = 33.53(1) A, α 2 = 93.36(5) °, β 2 = 90 °, γ 2 = 90 °. The mismatch of periodicities occurs along the a-direction. The structure consists of an alternated stacking of SmS (NaCl structure type) and (TiS 2 ) 2 slabs along the c-direction. Presence of interstitial Ti atoms within the van der Waals gap between adjacent TiS 2 layers is revealed. Thus, the stacking mode within the (TiS 2 ) 2 block is markedly different from that observed with misfit bilayer homologues such as (PbS) 1.18 (TiS 2 ) 2 or (SbS) 1.15 (TiS 2 ) 2 where no extra Ti atoms were found. Electrical transport measurements show a metallic behaviour down to 4.2 K. Magnetic study shows a behaviour mainly due to the Sm 3+ van Vleck paramagnetic ion.