Charge Transfer Complex of Hexakis (Alkylthio) Benzene with Tetrafluorotetracyanoquinodimethane (tEDTB) 2 TCNQF 4
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CHARGE TRANSFER COMPLEX OF HEXAKIS (ALKYLTHIO) BENZENE WITH TETRAFLUOROTETRACYANOQUINODIMETHANE (tEDTB) 2 TCNQF 4. CHASSEAU D.*,
ALLEAUME
M.*,
BRAVIC G.*,
LAPOUYADE R.**,
MORAND J.P.**,
AMIELL J.*** and DELHAES P.***
* Laboratoire de Cristallographie et Physique Cristalline, URA 144 CNRS ** Laboratoire de Photophysique et Photochimie Mol~culaire, URA 348 CNRS
et
ENSCP Bordeaux *** Centre de Recherche Paul Pascal CNRS Domaine Universitaire de Bordeaux I, 33405 - TALENCE C6dex ( FRANCE). Abstract In order to evaluate the potentiality of organic donor molecules for molecular organic ferromagnets, with in principle C molecular symmetry, as in the hexakis (alkylthio) benzene, we have prepared single crystals of the charge transfer complex of tris [ethylene dithio] benzene (tEDTB) with TCNQF 4 , which have been subsequently oxidized with bromine and arsenic pentafluoride gas. The stoichiometry of this complex is 2:1 and it crystallizes in the triclinic system, space group PT with the following cell parameters: a=11.515, b=11.044, c=10.460 A, a=111.50°, P=122.50°, -=93.820. The crystal structure consists of columns of alternating donor dyads and acceptors monads (DDADDA). The degree of charge transfer is estimated to be 0.2-0.3 from the methods based on bond lengths. While (tEDTB) 2 - TCNQF 4 does not give a significant ESR spectrum, after treatment with the bromine or AsF 5 gas, a single intense line, centered around the free electron g value, appears without any evidence of either a ground or an excited triplet state. Introduction In contrast to the considerable achievements that have occurred with electrical conductivity, and especially superconductivity, in organic materials, organic ferromagnets still remain a challenge. Meanwhile, several theoretical models have been proposed to realize ferromagnetic coupling in an organic solid [1]. From the structural standpoint Breslow [2], Miller et al. [1] and Yoshida et al.[3] use a donor (acceptor) component with one pair of degenerate highest occupied (lowest unoccupied) molecular orbital, to prepare mixed stacks of charge transfer (CT) complexes, whereas Torrance et al. [4] and Dormann et al. [5] explore segregated stacks of all donors (acceptors) as commonly found in electrically conducting radical ion salts. We have previously synthetized the following hexakis (alkylthio) benzenes (tEDTB, tVDTB) and tris (ethyleneoxythio) benzene (tEOTB) [6] and have already published some magnetic properties of a radical cation salt [7] and of a charge-transfer complex [8]. In order to assess the relevance of these molecules as possible precursors for molecular ferromagnets, we have now measured the physical properties at different oxidation states in solution and in the solid state of tEDTB complexed with TCNQF 4. The X ray crystal structure of (tEDTB) 2 TCNQF 4 has been refined. Synthesis and Molecular Composition Acetonitrile solutions of tEDTB and TCNQF 4 are mixed at room temperature and the solvent is slowly evaporated. Black crystals deposit first when TCNQF 4 is in large
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