An Unprecedented Self-Assembled Porous Framework Constructed by Intermolecular S…S Contacts
Bulletin of the Korean Chemical Society (Print)
In contrast to the polar hydrogen bond donor-acceptor pairs, thiol-containing moieties are not regarded as good hydrogen bond tectons due to their insufficient polarity. 1 On the other hand, although it is not directional, the intermolecular S···S interaction can be used in forming functional molecular assemblies as exemplified in the sulfur-rich molecular complexes of 4,5-bis(ethylenedithio)tetrathiafulvalene (ET) and metal-bisdithiolene complexes. 2 These intermolecular charge transfer
... rge transfer complexes need close contacts in solid states to exhibit electrical conductivity or magnetic properties, and the S···S interactions provide favorable interactions among the molecular components. The significant strength of this intermolecular interaction originates from a complementary electrophile-nucleophile interaction, or can be explained by a polar flattening model. 3,4 It is envisioned that S···S interactions will lead to more examples showing molecular assemblies in the solid state. Herein, we report the synthesis and crystal structures of the asymmetrical FcVET compound (Fc = ferrocenyl; VET = (4,5vinylenedithio-4',5'-ethylenedithio)tetrathiafulvalene) which has a unique integrated structure linked by intermolecular S···S interactions. We previously reported the synthesis and properties of a symmetrical diferrocenyl-VT compound (VT = 4,5-bis(vinylenedithio)tetrathiafulvalene), which is a sort of modified ET-donor with additional Fe(II)/Fe(III) redox properties. 5,6 As the electron donating property of VT is affected by Fc, we introduced a ferrocenyl moiety asymmetrically to a VET backbone to make the asymmetrical ferrocenyl-ET compound (FcVET). The typical phosphite-based crosscoupling reaction (Scheme 1) provided the FcVET donor molecule with a moderate yield, and the final product was fully characterized. 7 The red-orange single crystals of FcVET were grown in a mixed CH 2 Cl 2 /MeOH solvent pair by a slow diffusion method. The single crystals with lengths of 3-10 mm have a hexagonal-rod morphology (Figure 1 ), implying the directional packing of the molecules in the crystal lattice. The single crystal X-ray analysis shows that the unit cell belongs to a trigonal system defined as a hexagonal unit cell setting with very long aand baxes and a short c-axis. 8 The asymmetric unit is composed of an FcVET molecule and occluded solvent molecules: FcVET·(CH 2 Cl 2 ) 1/6 (CH 3 OH) 1/3 . The molecular structure of FcVET has two kinked sulfides (S3 and S4) bridging two ethenyl groups in the sixmembered 1,4-dithiin ring and almost flat sulfides (S7 and S8). As the four sulfides in the middle of the molecule (S1, S2, S5 and S6) are slightly kinked, the overall conformation of the VET moiety is curved (Figure 2 ). In the crystal lattice, two enantiomeric FcVET molecules form a pair in head-to-tail mode with inversion symmetry, which is stabilized by two intra-dimer S1···S2 * (3.579(5) Å; Scheme 1. Synthesis of FcVET. Figure 1. Photograph of FcVET·(solv)x single crystals. The inset shows a clear-cut hexagonal side view.