J. Rouxel

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.

Characterization of new “SnNbS3, PbNbS3, PbNb2S5, SnTiS3 and SnTi2S5” compounds

Abstract New MM′S3 and MM′2S5 phases (with M = Sn, Pb; M′ = Ti, Nb) have been characterized. They all exhibit an orthorhombic symmetry with a crystal structure related to the LaCrS3 structural type. Resistivity measurements indicate a metallic type behavior.

Structural aspects and magnetic properties of the lamellar compound Cu0.50Cr0.50PS3

Abstract Cu 0.50 Cr 0.50 PS 3 is a new lamellar compound obtained from the elements at 700°C in evacuated silica tubes. The unit cell is monoclinic with a = 5.916 (1) A; b = 10.246 (2) A; c = 13.415 (5) A; β = 107.09 (3)°. The structure is built up with S|Cu 0.33 Cr 0.33 (P 2 ) 0.33 |S slabs in which copper, chromium, and (P 2 ) pairs share the octahedral voids between two sulfur layers. Copper is not located at the center of its octahedral sites but is distributed among a continuous series of positions within these sites. This complex distribution has been simulated, attributing to copper two crystallographic eightfold positions with important thermal factors, especially perpendicular to the a - b plane. EPR studies and optical and magnetic measurements show that chromium is present as Cr 3+ ions. The magnetic study suggests that, below T N ∼ 30 K, this compound is a weakly anisotropic antiferromagnet consisting possibly of ferromagnetic layers which are antiferromagnetically coupled to adjacent layers. A good fit with the experimental results is obtained by means of calculations performed on the basis of a two-dimensional Heisenberg model.

Anionic polymeric bonds in transition metal ditellurides

Whereas sulfur and selenium tend, in some dichalcogenides, to bond to give ( X 2 ) 2− or ( X 2 ) − pairs, tellurium is more prone to setting multiple bonds. Reported CdI 2 -like and pyrite-like ditellurides are actually polymeric modifications leading to two new structural subgroups within these two families. A structures classification taking into account the dimensionality and the polymerization degree of such materials is suggested. A consequence of such anionic behavior is the occurrence of a partial oxidation state of tellurium, a frequent response of that element to a very stable cationic oxidation state. From many examples, it is shown that the polymerizing behavior of that heavy chalcogen anion seems to be much more general than expected and should lead to many charge transfer studies.

Chimie douce with solid precursors, past and present

This contribution deals with the evolution of chimie douce with Solid Precursors during the last twenty years through its two main components (i) redox intercalation deintercalation reactions (ii) acid-base processes based on exchanges, protonation of sites, and structural reconstruction from building blocks. In both cases a critical discussion of the present situation is made whereas possible evolutions for the next future are discussed.

Iron-intercalated molybdenum disulfide obtained from single-layer dispersion

MoS[sub 2] intercalation compounds with transition metals could be of great interest for catalysis of petrochemical processes, and also from the magnetic point of view since, for two-dimensional metallic layers included into a diamagnetic matrix, unusual magnetic properties can be expected. Iron-intercalated molybdenum disulfide, obtained by flocculation of a MoS[sub 2] single-layer dispersion in the presence of ferrous sulfate, was studied by electron microscopy and Moessbauer spectroscopy. Iron was found to occur at both II and III oxidation states between the MoS[sub 2] layers. The formation mechanism of this intercalated compound and its composition are discussed.

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 and properties of the new phase of the pseudo one-dimensional compound TaS3

Abstract The structure of a new form of tantalum trisulfide has been determined from single crystal X-ray diffraction data and refined to an R value of 0.025. The unit cell is monoclinic with space group P2 1 m : a = 9.515(2) A, b = 3.3412(4) A, c = 14.912(2) A, β = 109.99(2)°. The structure consists of sulfur triangular prisms stacked on top of each other by sharing triangular faces. The tantalum atoms are located close to the center of the prisms which are parallel to the b twofold axis. The prisms are linked together in the c direction to form slabs parallel to the b-c plane. This arrangement is very like that observed in NbSe3. The physical properties, especially the metal-semiconductor transition at 240 K, are discussed according to the structural features such as metal-metal distances and the existence of different SS pairs.

Ta4P4S29: A new tunnel structure with inserted polymeric sulfur

Abstract Ta 4 P 4 S 29 was prepared from the elements heated together in stoichiometric proportions in an evacuated Pyrex tube for 10 days at 500°C. The crystal symmetry is tetragonal, space group P 4 3 2 1 2, with the cell parameters: a = b = 15.5711(7) A, c = 13.6516(8) A, V = 3309.9(5) A 3 , and Z = 4. The structure calculations were conducted from 2335 reflections and 146 variables, leading to R = 0.033. The structure basic framework, corresponding to the chemical composition [TaPS 6 ], is made of biprismatic bicapped [Ta 2 S 12 ] units (average d TaS = 2.539 A), including sulfur pairs (average d SS = 2.039 A), bonded to each other through [PS 4 ] tetrahedral groups (average d PS = 2.044 A) sharing sulfurs. This framework leaves large tunnels running along the c axis of the cell and in which (S 10 ) ∞ sulfur chains are found to be inserted (average d SS = 2.052 A and SSS = 105.75°). Diamagnetic and semiconducting Ta 4 P 4 S 29 can be formulated: Ta V 4 P V 4 (S −II ) 16 (S −II 2 ) 4 (S 0 5 ).

Properties of the transition metal dichalcogenides: The case of IrS2 and IrSe2

The syntheses and structure determination of IrSe{sub 2} and IrS{sub 2} were undertaken. Pure phases were obtained and powder data were measured on an X-ray diffractometer. Rietveld refinement was successfully carried out for both structures (IrSe{sub 2}, 269 observations R (weighted profile) 0.062; IrS{sub 2}, 205 observations R (weighted profile) 0.074). The Pnam space group (No. 62) was found to yield the best results, eliminating Pna2{sub 1} as the other possible space group considered in a previous study of IrSe{sub 2}. Chalcogen pairs are found in both structures and these may correspond, in a first approach, to the charge balance Ir{sup 3+}X{sup 2{minus}}(X{sub 2}){sup 2{minus}}{sub 1/2}. However, long bond lengths were found in the chalcogen pairs (S-S 2.299(11) {angstrom}, Se-Se 2.555(4) {angstrom}) along with an unexpectedly small effective cationic radius of 0.50 {angstrom} for Ir{sup 3+}. These features of IrS{sub 2} and IrSe{sub 2} are discussed.