C. Hauw

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.

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.

Neutron diffraction and small-angle scattering studies of graphite-nickel chloride intercalation compounds

Abstract Intercalation of graphite with metal chlorides leads to compounds for which chemical analyses give non-integer stoichiometric coefficients. In particular, an excess of chlorine is observed with respect to free metal chlorides. For NiCl 2 intercalated graphite, the composition of the second-stage compound corresponds to the formula: C 11.3 NiCl 2.13 . This chlorine excess was accounted for by assuming the existence of small islands of intercalated chloride. As NiCl 2 -graphite compounds are known to undergo a magnetic phase transition at about 20K, neutron scattering and diffraction experiments were carried out in order to provide evidence for the islands and to specify the magnetic ordering at low temperature. From the small-angle scattering data collected below and above the magnetic transition, the first experimental evidence for the presence of intercalated islands has been obtained. The mean size of the islands is about 150 A, as previously assumed. From diffraction experiments, it has been shown that the spins of Ni 2+ ions in the magnetic phase are aligned ferromagnetically within the intercalant layer.

A metal-insulator phase transition close to room temperature: (BEDTTTF)2SbF6 and (BEDTTTF)2AsF6

Abstract We report the synthesis and characterization of two new salts of BEDTTTF: (BEDTTTF)2SbF6 and AsF6. Near to room temperature these two salts show a strong anomaly of conductivity, also visible on the EPR results. The crystal structure of the high temperature phase is described and a short discussion of the nature of the metal-insulator phase transition is given.

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.

Charge transfer in acceptor graphite intercalation compounds

We briefly review the various charge transfer mechanisms proposed for acceptor-graphite compounds. As there is no general consensus regarding even the amount of charge transfer in the case of bromine-GIC, we have studied the charge transfer during bromine desorption, using an empirical relationship based on CC bond lengths. The data show a maximum of charge transfer for stage-4 samples, which could correspond to the presence of Br2− entities.

Structure of Alkali-Metal-Doped Polyacetylene

Abstract The crystal structures of Li, Na, K and Cs doped (CH)x have been determined by X-ray diffraction and crystal packing analyses. The intercalation model, already proposed for iodine doping, is shown to account for the X-ray data.

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.