J. Gaultier

Intercalation compounds of graphite with nickel chloride: synthesis, structure, and mechanism of intercalation

Abstract The intercalation of nickel chloride into graphite in presence of chlorine gas has been studied in the temperature range 390 – 750 °C with an apparatus allowing the measurement of the chlorine pressure during intercalation. The results indicate that chlorine takes part in the reaction with a 600 mmHg threshold pressure below which no intercalation occurs. Between 495 and 690 °C, a second stage compound C 11.3 NiCl 2.13 , is obtained with the apparent activation energy of the intercalation being about 50 kcal/mole. X-ray investigations show that intercalated nickel chloride has a structure very close to the nickel chloride sandwich in free metal halide. However, intercalant layers are not complete, with the filling coefficient being at most 0.71. All of the data are consistent with an islandic nature of nickel chloride: islands of diameter 100 A allow explanation of the non integer stoichiometric coefficients given by chemical analyses and the amount of charge transferred from graphite to nickel, which is, moreover, consistent with a decrease of CC bond lengths as observed by X-ray diffraction.

Synthesis, structure and preliminary results on electrical and magnetic properties of (Perylene)2 [Pt(mnt)2]

Abstract In this paper we report the preparation, crystal structure and some physical properties of the conducting molecular (Perylene)2 [Pt(S4C4(CN)4)]. The crystal structure consists of segregated stacks of perylene and Pt S4C4 (CN)4 units, with a spacing of 3.3 A between the carbon atoms in the perylenes. The temperature dependence of the electrical conductivity is metallic with a maximum at approximately 15 K. At this temperature a sharp transition to an insulating state occurs. Magnetic suceptibility measurements confirm the existence of a transition in this temperature range.

Charge transfer and islands in metal halides-graphite intercalation compounds: New evidence from x-ray diffraction of intercalated Mn Cl2

Abstract Single crystal structure studies at room temperature have been made for the first stage Mn Cl 2 intercalated graphite. The nominal composition was C 5·6 Mn Cl 2·4 , as deduced from chemical analyses and X-ray diffraction intensities. The data are in agreement with the island model, already proposed for Ni Cl 2 intercalation. From the decrease in C-C bond length and comparison with As F 5 compound, it is shown that the charge transfer is determined by chlorine in excess with respect to free metal halide.

Etude par diffraction es rayons x et microscopie electronique a haute resolution de quelques composes d'insertion graphite-chlorure metallique

Resume X-ray diffraction and high resolution electron microscopy studies have been carried out on single crystals of Madagascar natural graphite intercalated with several metal halides: NiCl 2 , MnCl 2 and CuCl 2 . The structure of the second stage CuCl 2 compound is reported. Then the results obtained for the three metal chlorides are compared.

On the Structure and Properties of TMTTF and TMTSF Salts: Experimental Evidence for the Importance of Interchain Couplings

Abstract The structure and physical properties of tetramethyl-tetrathiofulvalene (TMTTF) salts are reviewed. New results are given about (TMTTF)2 PF6, (TMTTF)2 ClO4 and the selenium analog (TMTSF)2 ClO4. An experimental relationship is shown between the electrical and magnetic properties and the closest contacts S-S or Se-Se of neighbouring stacks.

A new class of conducting organo-metallic salts: TTF radical cation salts with metal halides

Abstract A new series of semi-conducting organo-metallic salts derived from tetrathiafulvalene (TTF) has been prepared by the electro-oxidation technique: (TTF) (MnCl3−)−0.75 ( σ RT ⋍ 15 Ω −1 cm −1 ), ( TTF ) ( MnCl 4 −− ) ⋍0.25 ( σ RT ⋍ 0.2 Ω −1 cm −1 ) and (TTF)(CoCl4−−)⋍0.25 ( σ RT ⋍ 0.2 Ω − cm − ). Preliminary X-ray work has shown that the first compound presents both regular TTF stacks and parallel inorganic chains. All of these compounds are strong paramagnets exhibiting antiferromagnetic interactions at low temperatures.

Pressure dependence of the structural and electronic properties of the molecular superconductor, (BEDT-TTF)2Cu(NCS)2

Abstract We report the compressibility tensor calculated from the pressure dependence ( The magnitudes of the principal compressibilities ki decrease very slightly and the bulk modulus strongly increases with increasing pressure. k2 is along the crystallographic b axis. Thus, the directions of the smallest(k3) and largest (k1) are in the ac plane; on the projection along the b axis, k3 is parallel to the long axis of the molecule and corresponds to the maximum density of atoms. The crystal structure of a twinned crystal has been refined to R = 0.095. Using the atomic coordinates, the transfer integrals have been calculated; the comparison of the high and ambient pressure band structures shows that the two-dimensional character of this compound is enhanced by pressure.

Mixed valence polyiodides from tetraphenyldithiapyranylidene: Crystalline structure and optical properties

Abstract Two conducting polyiodide salts have been obtained by direct oxidation of the donor DIPSO 4 by iodine. These salts are characterized by X-ray diffraction, Raman and optical spectroscopy. The nature of iodine species is determined and the degree of charge transfer is evaluated.

Low Temperature and High Pressure (1.7K & 7 102 MPa) Structure of the First Superconducting Organic Salt (TMTSF)2 PF6

Abstract The neutron (1. =1.1750A) high pressure (7 102MPa) and low temperature (1.7K) structure of (TMTSF)2PF6 (Di(2,3,6,7-tetramethyl-1,4,5,8-tetraselenafulvalenium hexafluorophosphate; 2(C10H12Se4)1/2+, PF6 −, Mr=1041.06) is reported. The lattice is triclinic P and cell parameters: The geometry of the Tmtsf stacks changes little under constraint exception made for a shortening in the interplanar spacing. For the titled compound at 7 102 MPa a temperature decrease from 300K to 4K is equivalent to the effect of an extra 2 102MPa applied pressure. However temperature (rather than pressure) is responsible for a small change in the transverse shift of adjacent Tmtsf molecules in a same column. Similarly pressure has little effect on the PF6 − anion disorder at a given temperature. If the low temperature TMTSF packing of (TMTSF)2PF6 (superconducting below ≃ 1.2K and above 9.5 102 MPa) is compared to that of (Tmtsf)2 C104 (superconducting below ≃1,2K at ambient pressure), the intrachain interactions are found...

Structure of Di-Tetramethyltetraselen-afulvalenium Perchlorate (TMTSF)2 CϱO4 in its Low Temperature (T ∼ 10 K) Ordered Phase

Abstract At T ∼ 24K, the quasi one dimensional organic superconductor (TMTSF)2CϱO4 shows a structural transition leading to a doubling (a × 2b × c) of the unit cell. The neutron average structure (i.e. superlattice reflections not included) at T = 7K has already been published. In the present paper, we report the results of a rigid body refinement of the low temperature (T ∼ 10K) structure from both the earlier set of neutron main reflection intensities and an extra set of X-ray superlattice intensities. This improved structural description clearly shows that the anion orientations alternate in the b direction only and that there is no significant TMTSF displacement from the average position. We compare these results with recent structural data obtained on (TMTSF)2ReO4 which exhibits below T ∼ 180 K an insulating ground state instead of the metallic one for the perchlorate salt.