CLATHRATE FORMATIONS WITH ISOMERIC HOST COMPOUNDS BASED ON THIENO[3,2-B]THIOPHENE AND THIENO[2,3-B]THIOPHENE - INCLUSION MODES AND CRYSTAL-STRUCTURES

Two host compounds 1 and 2, which are composed of isomeric thieno[3,2-b]thiophene and thieno[2,2-b]thiophene, respectively, afforded crystalline host-guest inclusion complexes. Benzene and DMSO were chosen as guest species capable of the least and the most intense host-guest interactions, respectively, and the X-ray crystal structures of their clathrates were investigated. Benzene was enclathrated in each of 1 and 2 with different host-to-guest ratios to give (1)(3)(benzene)(4) and(a)(benzene). In both crystals, there are pairs of benzene molecules arranged in parallel offset. Crystal data: (1)(3)(benzene)(4), triclinic, P $($) over bar$$ 1, a = 13.940(5)Angstrom, b = 15.537(2)Angstrom, c = 13.040(4)Angstrom, alpha = 104.13(2)degrees, beta = 119.91(2)degrees, gamma = 92.24(2)degrees, V = 2330(1)Angstrom(3), Z = 1; (2)(benzene), triclinic, P $($) over bar$$ 1, a = 12.427(4)Angstrom, b = 13.041(4)Angstrom, c = 10.733(2)Angstrom, alpha = 92.97(2)degrees, beta = 104.79(2)degrees, gamma = 117.10(1)degrees, V = 1648.2(7)Angstrom(3), Z = 2. The(2)(benzene) crystals eliminate the guest at significantly high temperature, 128 degrees C, which is discussed in light of the hydrogen-bonded rigid host lattices. The crystals including DMSO, (1)(DMSO)(2), and (2)(DMSO)(2) were isomorphous. Crystal data: (1)(DMSO)(2), triclinic, P $($) over bar$$ 1, a = 12.618(1)Angstrom, b = 13.161(2)Angstrom, c = 11.615(3)Angstrom, alpha = 115.41(2)degrees, beta = 97.04(2)degrees, gamma = 103.41(1)degrees, V = 1639.7(6)Angstrom(3), Z = 2; (2)(DMSO)(2), triclinic, P $($) over bar$$ 1, a = 12.613(1)Angstrom, b = 13.383(3)Angstrom, c = 11.601(2)Angstrom, alpha = 115.49(1)degrees, beta = 97.28(1)degrees, gamma = 104.60(1)degrees, V = 1647.3(5)Angstrom(3), Z = 2. The formation of the isostructural crystals is discussed on the basis of the strong hydrogen bonding between the host and guest molecules, which counteracts the structural and electronic differences between 1 and 2. In line with this interpretation, the conformational preference of the OC-CS bonds due to the electrostatic O ... S attraction was overcome in the DMSO inclusion crystals. In spite of the isostructural crystal packing, their thermal behavior of guest release, as investigated by DSC measurements, is rather different; (1)(DMSO)(2) loses the guest DMSO molecules stepwise at 111 and 138 degrees C, whereas (2)(DMSO)(2) does at 96 and 159 degrees C.