Crystallography Reports, Vol. 49, No. 6, 2004, pp. 1010–1017. Translated from Kristallografiya, Vol. 49, No. 6, 2004, pp. 1107–1114. Original Russian Text Copyright © 2004 by Zorina, Khasanov, Shibaeva, Shevyakova, Kotov, YagubskiÏ. STRUCTURE OF ORGANIC COMPOUNDS Crystal Structure of the New Radical Cation Salt (DOET)4[Fe(CN)5NO]1.25(C6H5Cl)0.75 L. V. Zorina*, S. S. Khasanov*, R. P. Shibaeva*, I. Yu. Shevyakova**, A. I. Kotov**, and É. B. YagubskiÏ** * Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, NoginskiÏ raÏon, Moscow oblast, 142432 Russia e-mail: [email protected] ** Institute for Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, NoginskiÏ raÏon, Moscow oblast, 142432 Russia Received August 1, 2003 Abstract—A new radical cation salt based on 4,5-(1,4-dioxanediyl-2,3-dithio)-4',5'-ethylenedithiotetrathiaful- 2– valene (DOET) with the photochromic anion [Fe(CN)5NO] , namely, (DOET)4[Fe(CN)5NO]1.25(C6H5Cl)0.75, is synthesized. Single crystals of this salt are studied using X-ray diffraction [a = 10.398(2) Å, b = 11.168(2) Å, c = 18.499(4) Å, α = 103.14(3)°, β = 92.80(3)°, γ = 106.02(3)°, V = 1996.3(7) Å3, space group P1 , and Z = 1]. In the structure, radical cation layers alternate with anion layers along the c axis. The centrosymmetric dimers are formed by DOET radical cations in the donor layer with packing of the β type. Like the vast majority of DOET-based salts, the new salt possesses semiconductor properties. © 2004 MAIK “Nauka/Interperiodica”. INTRODUCTION this series of investigations and studied a new salt based on the donor 4,5-(1,4-dioxanediyl-2,3-dithio)-4',5'-eth- In recent years, considerable research attention has ylenedithiotetrathiafulvalene (DOET), C H S O . been focused on the design of new synthetic functional 12 10 8 2 (conducting and magnetic) materials that can serve as S S an alternative to traditional conductors and magnets. S S These materials are promising for technical application in new fields of engineering due to their specific fea- S S S S tures and (or) an unusual combination of properties. BEDT-TTF From this point of view, molecular organic conduc- S S O tors are especially interesting objects of investigation. S S Materials based on organic molecules exhibit a great variety of conducting properties. Among these materi- S S S S O als are semiconductors, stable metals, and supercon- DOET ductors with the highest superconducting transition The modification of parent donor molecules is an temperature TC = 14.2 K [1–4]. The unique properties manifested by compounds of this class have stimulated efficient method for synthesizing new salts, which a purposeful search for new methods of synthesizing allows an understanding of the influence of the donor multifunctional molecular materials with controlled nature on the structure and properties of organic con- properties, in particular, through introducing anions ductors. The majority of organic conductors and super- with specific physical properties into a conducting conductors were prepared on the basis of the organic organic matrix. donor BEDT-TTF. The DOET molecule differs from the BEDT-TTF molecule by an additional six-membered Following this idea, we synthesized and investigated heterocycle containing two oxygen atoms. Owing to a number of new radical cation salts with the photo- the presence of this heterocycle in the DOET molecule, 2– chromic nitroprusside anion [Fe(CN)5NO] on the first, the total number of heteroatoms increases and, basis of different π-electron organic donors, such as hence, the probability of forming side intermolecular bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) [5– contacts of the heteroatom···heteroatom type (in partic- 8], bis(ethylenedioxo)tetrathiafulvalene (BEDO-TTF) ular, additional contacts S···O and C···O) that provide [5, 9], ethylenedithiotetrathiafulvalene (EDT-TTF) interaction in the radical cation layer is higher. Second, [5, 10], bis(dithiolanylidene)tetrathiapentalene (BDH- the presence of oxygen atoms leads to the formation of TTP) [11], tetrathiotetracene (TTT), and tetraselenotet- C–H···O hydrogen bonds between the neighboring rad- racene (TSeT) [12]. In the present work, we continued ical cations. 1063-7745/04/4906-1010 $26.00 © 2004 MAIK “Nauka/Interperiodica” CRYSTAL STRUCTURE OF THE NEW RADICAL CATION SALT 1011 A distinguishing feature of the DOET molecule is its dc power supply. A platinum wire 1 mm in diameter strongly bent shape: carbon atoms of the oxygen het- was used as electrodes. erocycle form a plane nearly perpendicular to the plane Electrocrystallization was performed under direct of the central skeleton of the molecule. The formation current conditions (I = 0.5 µA) at a temperature of 25°C of such a conformation can easily be explained in terms for 12 days. Crystals grew on the anode in the form of of the geometry of bonds. In the BEDT-TTF molecule, black plates approximately 0.8 × 0.9 × 0.07 mm3 in all carbon atoms, except for the carbon atoms involved size. The crystals were filtered off, washed thoroughly in the outer ethylene groups, are characterized by a pla- with acetone, and dried in air. 2 nar Csp configuration. In the oxygen heterocycle of the DOET molecule, both the outer and inner C–C bonds X-ray Diffraction Analysis 3 are single bonds and the stable Csp electronic state of The main crystal data are as follows: a = 10.398(2) Å, the corresponding carbon atoms is provided by the b = 11.168(2) Å, c = 18.499(4) Å, α = 103.14(3)¡, β = attachment of an additional hydrogen atom. Therefore, 92.80(3)¡, γ = 106.02(3)¡, V = 1996.3(7) Å3, space the inner carbon atoms of the oxygen heterocycle adopt group P1 , Z = 1 for the formula composition a bulk tetrahedral coordination, which, in turn, deter- C H Cl Fe N O S , M = 2125.1, mines the bond directionality and the molecular shape. 58.75 43.75 0.75 1.25 7.5 9.25 32 ρ 3 µ F(000) = 1080, calcd = 1.768 g/cm , and (MoKα) = The influence of the specific features revealed in the 11.54 cm–1. The experimental set of diffraction data molecular structure of the DOET radical cation on the involving 7336 reflections (6999 unique reflections, structure and properties of the salts synthesized will be Rint = 0.012, Rσ = 0.022) was collected on an Enraf– demonstrated by using the example of a new radical cation Nonius CAD4 automated diffractometer (MoKα radia- salt, namely, (DOET)4[Fe(CN)5NO]1.25(C6H5Cl)0.75. In tion, λ = 0.71073, graphite monochromator, θ = 2.5¡Ð this work, we described the synthesis of the aforemen- 25.0¡, ω scan mode) at room temperature. The structure tioned new radical cation salt, performed an X-ray dif- was solved by direct methods with subsequent Fourier fraction analysis of its crystal structure, and investi- syntheses according to the SHELXS97 software pack- gated the conducting properties of the single crystals. age [16] and refined by the full-matrix least-squares procedure with the SHELXL97 software package [17]. All non-hydrogen atoms (except for the disordered EXPERIMENTAL atoms in positions with a low occupancy in the DOET molecule I and the anion) were refined in the anisotro- Synthesis of (DOET)4[Fe(CN)5NO]1.25(C6H5Cl)0.75 pic approximation. The hydrogen atoms were located from geometric considerations with the isotropic ther- 4,5-(1,4-Dioxanediyl-2,3-dithio)-4',5'-ethylenedi- mal parameters UH = 1.2UC. The final R factor is equal thiotetrathiafulvalene (DOET) was synthesized accord- to 0.056 and GOOF = 1.047 for 5483 unique reflections ing to the procedure described in [13] and purified chro- with I > 2σ(I) for 699 parameters refined. matographically. Potassium nitroprusside K2[Fe(CN)5NO] · 2H2O was prepared using the proce- dure proposed in [14]. Chlorobenzene (Aldrich) was Conductivity Measurements twice distilled over P2O5. 18-Crown-6 (Flucka) was The conducting properties were investigated on an purified by recrystallization in acetonitrile and dried automated setup in the temperature range 315–4.2 K. under vacuum at a temperature of 30°C. Ethanol (Ald- The resistance was measured by the standard four-point rich) was allowed to stand for 10 h over freshly calci- probe method under direct current along the long crys- nated calcium oxide at the boiling temperature (78.3¡C) tal edge, which coincides with the a axis. The sample and was then distilled. All the solvents used were stored was cemented to platinum wires (10 µm in diameter) of in an inert atmosphere. the measuring unit with the use of a conducting graph- ite paste (Dotite paint, XC-12). The (DOET)4[Fe(CN)5NO]1.25(C6H5Cl)0.75 radical cation salt was prepared by electrochemical oxidation of DOET in the presence of a K2[Fe(CN)5NO] · 2H2O RESULTS AND DISCUSSION × –3 supporting electrolyte [15]. DOET (1.14 10 mol/l) and The (DOET)4[Fe(CN)5NO]1.25(C6H5Cl)0.75 crystals × –3 a mixture of K2[Fe(CN)5NO] · 2H2O (2.4 10 mol/l) have a layered structure in which the radical cation lay- with 18-crown-6 (4.9 × 10–3 mol/l) were placed in dif- ers alternate with the anion layers along the c axis. Fig- ferent arms of an H-shaped electrochemical cell and ure 1 shows the projection of the structure along the dissolved in a mixture of chlorobenzene (20 ml) with [110] direction. In the conducting donor layer, there are ethanol (1 ml). The dissolution was carried out at room two crystallographically independent radical cations temperature for 4 h in an argon atmosphere with contin- DOET I and II (Fig.