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A single crystal of the two-dimensional structure [NH3(CH2)4NH3]MnCl4 is studied by Electron Paramagnetic Resonance (EPR) when rotated around a ∗ , b and c axes, at X-band and room temperature. Magnetic susceptibility was also measured on a powder sample between 5 and 300 K. Intralayer exchange interaction J k = (4.6 ± 0.4) K calculated from anisotropy of the EPR linewidth is in good agreement with the value |J| k = (4.4 ± 0.1) K deduced from magnetic susceptibility measurements.

The X-ray absorption spectroscopy (EXAFS) technique has been used for studying the local environment of the metal in graphite intercalation compounds with transition metal dichlorides. For these compounds the octahedral environment of the cation is preserved after the intercalation process. A simulation of the first coordination shell with a two metal-ligand distance distribution enables the characterization of a strong distortion of the octahedra. The study of the radial distribution function around the metal atoms gives evidence of the existence of a second coordination shell.

The new charge transfer complex t-TTF-TCNQ, whose unsymmetric cation is intermediate between TTF and HMTTF, presents a regular stacking of both donor and acceptor chains. We show that this compound has a metallic behavior at high temperatures and undergoes one metal-insulator transition near 81 K. Its electrical and magnetic properties are examined in connection to this phase transition and the effective dimensionality.

In this paper we report the preparation, crystal structure and some physical properties of the conducting molecular (Perylene) 2 [Pt(S 4 C 4 (CN) 4 )]. The crystal structure consists of segregated stacks of perylene and Pt S 4 C 4 (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.

Magnetic susceptibility studies have been carried out on a series of polyacetylene samples doped with iron chloride either chemically or electrochemically at various doping levels. The data strongly indicate that the limiting stoichiometric coefficient for FeCl-4 is close to 0.05 and that chlorine is fixed at high doping levels. An intercalation model is proposed for the structure of these compounds, based on X-ray diffraction results and compatible with the composition found by magnetic studies.

The magnetic properties of M 2 Cu 2 O 5 (M = Y, Lu, Sc, In) have been investigated. The compounds have an antiferromagnetic ground state. The magnetic structure of Y 2 Cu 2 O 5 at 2K has been obtained using neutron diffraction. Cu 2+ ions are arranged in chains directed along the a-axis, which form isolated layers parallel to the (001) plane. The interplane coupling is antiferromagnetic, whereas two in-plane ferromagnetic couplings exist, one inside the chains (strong) and the other between the chains (weak).

We report the results of EPR studies on the ionic-radical salt (TEA) + (TCNQ) 2 - composed of an oganic free radical anion and a diamagnetic cation. Between about 40 and 80 K this crystal exhibits the triplet exciton EPR spectrum characteristic of an alternating chain of spins. The triplet spin Hamiltonian parameters are | D | = 44 ± 2 G and | E | = 5.5 ± 1 G. The directions of the zero field splitting principal axes are determined through single crystal rotation studies at 55 K and related to the crystal structure.

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.

The magnetic properties of graphite-MnCl2 intercalation compounds (stages 1 and 2) were investigated from 3 to 300K by EPR and static susceptibility experiments. The behaviour of the magnetic susceptibility anisotropy, EPR linewidth and g-factor gives evidence for short range order effects increasing sharply below 50K. The data are analyzed in connection with the two-dimensionality of the compounds.