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 crystal line host-guest inclusion complexes. Benzene and DMSO were chosen as g uest species capable of the least and the most intense host-guest inte ractions, respectively, and the X-ray crystal structures of their clat hrates 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 arran ged 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)An gstrom, 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 tem perature, 128 degrees C, which is discussed in light of the hydrogen-b onded rigid host lattices. The crystals including DMSO, (1)(DMSO)(2), and (2)(DMSO)(2) were isomorphous. Crystal data: (1)(DMSO)(2), triclin ic, P $($) over bar$$ 1, a = 12.618(1)Angstrom, b = 13.161(2)Angstrom, c = 11.615(3)Angstrom, alpha = 115.41(2)degrees, beta = 97.04(2)degre es, gamma = 103.41(1)degrees, V = 1639.7(6)Angstrom(3), Z = 2; (2)(DMS O)(2), triclinic, P $($) over bar$$ 1, a = 12.613(1)Angstrom, b = 13.3 83(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 molec ules, which counteracts the structural and electronic differences betw een 1 and 2. In line with this interpretation, the conformational pref erence of the OC-CS bonds due to the electrostatic O ... S attraction was overcome in the DMSO inclusion crystals. In spite of the isostruct ural crystal packing, their thermal behavior of guest release, as inve stigated 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.