Crystal engineering in p-overlapping stacks: unusual one- and/or two-dimensional stacking of the p -system in the crystal structure of the cation radical salts of tetrathiafulvalene vinylogues Electrochemical oxidation of 1 and 2 in chlorobenzene gave the cation radical salts 1·FeCl4, 1·ReO4 and 2·PF6·(H2O)8 as stable single crystals with stoichiometries of 1 : 1 (donor : anion). They show semiconducting behaviour‡ due to the integrally charged states. The X-ray crystallographic analyses for these salts were carried out, and crystal data and details of measurements are summarized in Table 1. The crystal structure of 1·FeCl4 salt is shown in Fig. 2. The pseudo two-dimensional stack of 1 along the c axis, which slightly differs from that of 1·PF6, was observed.The degree of overlap of the 1,3- benzodithiole parts in 1·FeCl4 salt decreases compared with the full -overlapping mode of the salt 1·PF6. This change in the two-dimensional stack of 1·FeCl4 salt may arise from the larger size of FeCl4 anion. Preliminary magnetic measurements of 1·FeCl4 salt with a superconducting quantum interference device (SQUID) showed an antiferromagnetic interaction.§ Masaaki Tomura* and Yoshiro Yamashita† Institute for Molecular Science, Modaiji, Okazaki 444-8585, Japan. E-mail: tomura@ims.ac.jp Received 25th April 2000, Accepted 18th May 2000, Published 24th May 2000 One- and/or two-dimensional p-overlapping stacks have been found in the crystals of the cation radical salts of the tetrathiafulvalene (TTF) vinylogues having o-substituted phenyl groups at the vinyl positions.The packing mode in the twodimensional p-stacks could be modified depending on the counter anions. For the development of functions such as electrical conductivities, magnetic properties, or non-linear optical properties in molecular crystals, not only the electronic properties of molecules themselves but also the molecular arrangements in the crystals are very important. Therefore, the design of crystal structures and control of molecular arrangements, i.e., crystal engineering, has attracted much attention in recent years.1–5 In the field of organic conductors and superconductors, the construction of multidimensional structures is regarded as a main strategy of stabilizing the metallic state at low temperature.6 The multidimensional architecture can be achieved by the introduction of chalcogen atoms into the peripheral positions of p-conjugated molecules.7,8 Sulfur–nitrogen interheteroatom contacts are also useful in constructing unique molecular networks.9 Another approach for construction of multi-dimensional structures is to use steric effects of bulky substituents.Inabe and Morimoto have reported two- and three-dimensional networks in neutral radical crystals of axially substituted dicyanophthalocyanines.10 We have recently succeeded in the isolation of the cation radical salts of tetrathiafulvalene (TTF) vinylogues 1 and its derivatives with extended p- conjugation and o-substituted phenyl groups at the vinyl positions.11,12 The X-ray crystallographic analyses of the salts have revealed the planar p-conjugated TTF vinylogue framework to which the bulky aryl groups are perpendicular.In the case of the cation radical salt 1·PF6, this unique molecular structure causes a two-dimensional overlapping mode where one molecule bridges two other molecules, as shown in Fig. 1. The bulky aryl groups disturb the formation of the usual one-dimensional stacking of 1. We have now examined the effect of the counter anion and the substituent on the 1,3-dithiole ring in the twodimensional stacks. In this communication, we report two types of the two-dimensional stacks in the cation radical salts of 1 and the one-dimensional grid-like stack in the cation radical salts of the ethylenedithio derivative 2.DOI: 10.1039/b003274n CrystEngComm, 2000, 14 Fig. 1 Crystal structure of 1·PF6 viewed along the b axis.Table 1 Crystal data and details of measurementsa for 1·FeCl4, 1·ReO4 and 2·PF6·(H2O)8b Property 1·FeCl4 C28H14Cl4F4FeS4 752.28 Triclinic Formula MCrystal system 1 P 7.3717(9) 11.978(3) 16.832(2) 87.83(1) 84.071(9) 83.70(1) 1468.8(4) 2 4 4 296(2) 10.533 (Cu-Ka) Space group a/Å b/Å c/Å a(°) b(°) g(°) U/Å3 ZTemperature/K m/mm–1 Measured reflections Unique reflections Rint 6270 5972 0.0676 0.0847 0.2225 R1 [F, I > 2 s(I)] wR2 [F2, I > 2 s(I)] a The data for 1·FeCl4 and 1·ReO4 were collected on an Enraf-Nonius CAD4 diffractometer using Cu-Ka radiation ( l = 1.54178 Å).Absorption corrections were applied using empirical procedures based on azimuthal y scans of seven reflections having an Eulerian angle, c, near 90°. The data for 2·PF6·(H2O)8 were measured on a Rigaku RAXIS IV imaging plate area detector using Mo-K radiation ( l = 0.71070 Å). An absorption correction was not applied. b All structures were solved by direct methods and refined by full-matrix least-squares on F2 with SHELX97.13 All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed geometrically and refined by using a riding model. Click here for full crystallographic data (CCDC no. 1350/20). Fig. 2 Crystal structure of 1·FeCl4 viewed from the direction perpendicular to the plane of the 1,3-dithiole rings. Click here to view the 3D crystal structure of 1·FeCl4.When a tetrahedral ReO4 anion was used as a counter ion, the structure of the two-dimensional stack drastically changed. Fig. 3 shows the crystal structure of 1·ReO4 salt. We found zigzag two-dimensional stacking with an angle of nearly 90° along the c axis (Fig. 3a). The side view of the crystal structure (Fig. 3b) clearly shows a stair-like unistacking structure where two-dimensional interactions can be expected. The interstack distance is 3.6 Å, which is the same as those of the cation radical salts 1·PF6 and 1·FeCl4. The ReO4 anions are located on the center of the four aryl groups which belong to the two stacks. Next we have changed the substituents on the 1,3-dithiole rings because they can affect the stacking structure of the cation radical salts.We have observed not the twodimensional p–p overlapping stack found in the cation radical salts of 1, but the one-dimensional stacking of p- system in the crystal structure of the cation radical salts 2·PF6·(H2O)8. Fig. 4 shows the crystal structure where the TTF vinylogue framework is stacked in a one-dimensional fashion along the [10 ] 1 direction. Within the overlap, the 2·PF6·(H2O)8 1·ReO4 C24H30F10O8PS8 923.94 Monoclinic C28H14F4O4ReS4 804.83 Monoclinic 4236(2) C2/c C2/c 27.421(4) 19.626(5) 14.414(4) 19.742(4) 7.404(3) 14.591(3) 90 90 100.99(3) 131.47(1) 90 90 2873(2) 296(2) 0.541 (Mo-Ka) 5869 2608 0.0000 0.0964 0.2565 296(2) 11.531 (Cu-Ka) 3165 2926 0.0274 0.0869 0.2334 (a) (b) Fig.3 Crystal structure of 1·ReO4: (a) viewed along the c axis, (b) view perpendicular to the stacking c axis; the ReO4 anions are omitted for clarity. Click here to view the 3D crystal structure of 1·ReO4. angle between the two long axes of the TTF vinylogue frameworks is 25°, and the shortest S···S contact between the one-dimensional stacks is 3.9 Å. The one-dimensional overlapping mode of 2 has brought a grid-like structure (Fig. 4b) with a void in which eight water molecules are occupied. The square grid appears by viewing along the c axis, and the dimensions of the grid are 7.5 Å (interstack distance between the TTF vinylogue framework) and 9.9 Å(a long side of the grid).The 1,3-dithiole rings in 2 are unfavorable for p–p intermolecular interactions due to less p-delocalization and steric interactions of the ethylenedithio parts compared to those in 1. This seems to lead to the novel one-dimensional structure, not the twodimensional one. The results described here suggest that control of a crystal packing using steric effects is an excellent strategy to realize unusual crystal structures. Studies on the isolation and the characterization of other cation radical salts of the TTF vinylogues 1 and 2, and related molecules are now in progress. (a) (b) Fig. 4 Crystal structure of 2·PF6·(H2O)8: (a) viewed along the [10] direction, (b) the grid-like structure viewed along the c axis.The water molecules are omitted for clarity. Click here to view the 3D crystal structure of 2·PF6·(H2O)8. Acknowledgements This work was supported by a Grant-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Science, Sports and Culture, Japan. We gratefully acknowledge Prof. Katsuya Inoue of the Institute for Molecular Science for his help in the SQUID measurements and Dr Ken-ichi Imaeda of the Institute for Molecular Science for conductivity measurements. References 1 G. M. J. Schmidt, Pure Appl. Chem., 1971, 27, 647. 2 G. R. Desiraju, Crystal Engineering: The Design of Organic Solids, Elsevier, Amsterdam, 1989. 3 Design of Organic Solids, ed. E. Weber, Springer- Verlag, Berlin, 1998.4 D. Braga, F. Grepioni and G. R. Desiraju, Chem. Rev., 1998, 98, 1375. 5 Crystal Engineering: from Molecules and Crystals to Materials, ed. D. Braga, F. Grepioni and A. G. Orpen, Kluwer Academic Publishers, Dordrecht, 1999. 6 Handbook of Organic Conductive Molecules and Polymers, ed. H. S. Nalwa, Wiley, Chichester, 1997, vol. 1. 7 J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser, H. H. Wang, A. M. Kini and M.-H. Whangbo, Organic Superconductors, Prentice Hall, New Jersey, 1992. 8 T. Ishiguro and K. Yamaji, Organic Superconductors, Springer-Verlag, Berlin–Heidelberg, 1990. 9 Y. Yamashita and M. Tomura, J. Mater. Chem., 1998, 8, 1933. 10 K. Morimoto and T. Inabe, J. Mater. Chem., 1995, 5, 1749. 11 Y. Yamashita, M. Tomura, M. B. Zaman and K. Imaeda, Chem. Commun., 1998, 1657. 12 Y. Yamashita, M. Tomura, S. Tanaka and K. Imaeda, Synth. Met., 1999, 102, 1730. 13 G. M. Sheldrick, SHELX97, Program for the structure solution and refinement of crystal structures, 1997, University of Göttingen, Germany. Footnotes † Present address: Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama 226-8502, Japan. E-mail: yoshiro@echem.titech.ac.jp ‡ 1·FeCl4: s = 1 × 10–2 S cm–1, Ea = 0.14 eV; 1·ReO4: s = 2.5 × 10–4 S cm–1, Ea = 0.19 eV. § Detail of the magnetic properties of the cation radical salt 1·FeCl4 will be reported elsewhere. CrystEngComm © The Royal Society of Chemistry 2000