Structure of 3,4;3',4'-bis(ethylenedithio)-2,2',5,5'-tetrathiafulvalenium–hydrogensulfate (3/2). A (BEDT-TTF) charge-transfer salt containing a tetrahedral anion

Abstract

3C10HsSs.2HSO4, M r = 1348.1, triclinic, P]-, a ----7.633 (1), b = 9.440 (1), c = 16.607 (1) A, ~t = 92.28(1), f l=94 .97(1) , y = 8 3 . 1 3 ( 1 ) °, V = 1181.8(3)A 3, Z = l , D x = l . 8 9 M g m -3, 2(MoKa) -0 .71073A, /1= 1.175mm -~, F(000)=686, T = 298K. Electrocrystallization of BEDT-TTF with [N(C4Hg)4][HSO41 in 1,1,2-trichloroethane yields a charge-transfer salt containing BEDT-TTF cations and (HSO4)anions in a 3:2 ratio. This product consists of segregated stacks of BEDT-TTF cations with (HSOa)anions located in the cavities formed by the H atoms associated with the ethylenedithiol groups of the BEDT-TTF donors. The asymmetric unit contains two crystallographically independent BEDT-TTF molecules in a lattice which is highly cross linked with multiple intermolecular S-S contacts _ O.Oa(Fo 2) and 289 variable parameters. Introduction. The use of X-ray and neutron diffraction data, in conjunction with tight-binding band calculations, has provided considerable insight into some of the factors governing the conductivity behavior of several organic charge-transfer compounds with metal-like magnetic and electrical properties. Among the most intensively studied systems are a large number containing tetrathiafulvalene or a derivative in which tetrathiaor tetraselenafulvalene forms part of the molecular framework (Williams, Wang, Emge, Geiser, Beno, Leung, Carlson, Thorn & Schultz, 1987). For one series of charge-transfer compounds containing bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) cations and linear centrosymmetric monovalent anions, a direct correlation between anion length and the onset temperature of superconductivity has been established (Emge, Leung, Beno, Wang, Firestone, Webb, Carlson, Williams, Venturini, Azevedo & Schirber, 1986). This type of correlation not only provides a means of fine-tuning the electrical properties of the system by the * To whom correspondence should be addressed. 0108-2701/87/112201-03501.50 judicious selection of anion, but also provides a pathway for the rational development of new materials with specific conductivity properties. As part of an ongoing project aimed at exploring structure-conductivity relationships in BEDT-TTF salts, we recently prepared a new product containing the monovalent (HSO4)anion. In this paper we report the room-temperature crystal structure of the 32 charge-transfer salt (BEDT-TTF)a(HSO4) 2. Experimental. Black multifaceted crystals of approximate dimensions 0.20 x 0.24 x 0.13 mm obtained by electrocrystallization of BEDT-TTF at a constant current of 0.42 laA in 1,1,2-trichloroethane using H-cells equipped with platinum electrodes and [N(C4H9)4][HSO 4] as the supporting electrolyte. Triclinic symmetry suggested on the basis of interaxial angles and confirmed by a Delaunay reduction. Refined cell parameters obtained from the setting angles of 25 reflections with 30 < 2 0 < 35 °. 0-20-scan data collection carried out at ambient temperature using a Nicolet P3F diffractometer and graphite-monochromated M o K a radiation. Scan rate variable, 212 ° min-~; scan range 1 . 2 ° in 20 from KGq to + 1-1 ° from Ka 2. 6648 reflections (_+8, _+10, +17)measured with 4_<20_<45 ° and averaged to give 3114 unique reflections with wR,, t = 0.021. Three standards (12i, 114, 212) measured every 47 data showed no significant variation over the period of data collection. The data were corrected for absorption, Lorentz and polarization effects. Absorption corrections applied using a Gaussian quadrature procedure following careful measurement of crystal dimensions and assignment of indices to the crystal faces. Minimum and maximum transmission 0.770 and 0.861, respectively. Structure solution and refinement carried out using a locally modified version of the UCLA collection of crystallographic software (Strouse, 1986). S-atom positions from MULTAN78 (Main, Hull, Lessinger, Germain, Declercq & Woolfson, 1978); remaining non-H-atom positions from difference-Fourier maps. H atoms associated with the BEDT-TTF donors were placed in idealized positions with fixed isotropic thermal © 1987 International Union of Crystallography