AN ISOMERIC SERIES OF THIOPHENE-FUSED TETRACYANOQUINODIMETHANES .2. THE CRYSTAL AND MOLECULAR-STRUCTURES

The crystal structures of three isomeric thiophene-fused TCNQs, 4,8-bis(dicyanomethylene)-4,8-dihydro-benzo[1,2-b:4,5-b']dithiophene(1),[1,2-b:5,4-b']isomer(2), and[1,2-b:4,5-c']isomer(3) have been determined by the X-ray method. The crystals of 1, 2, and 3 are an isostructure of the monoclinic system with the space group of P2(1)/n. For 1, a=16.588(3), b=7.222(5), c=11.353(3) angstrom, 8=89.88(2)-degrees, V=1360.1(10) angstrom3, Z=4, D(x)=1.545 Mg m-3. For 2 a=16.594(4), b=7.232(2), c=11.433(2) angstrom, beta=91.05(2)-degrees, V=1371.8(5) angstrom3, D(x)=1.532 Mg m-3. For 3 a=16.738(2), b=7.342(3), c=10.922(3) angstrom, beta=92.98(2)-degrees, V=1340.4(7) angstrom3, D(x)=1.568 MgM-3. These crystals show an orientational disorder with an approximate molecular symmetry of mm. The occupancy factors are 0.834:0.166, 0.709:0.291, and 0.5:0.1:0.15:0.25 for 1, 2, and 3, respectively. The final R values are 0.065, 0.070, and 0.096 for 2308, 2410, and 1566 observed reflections for 1, 2, and 3, respectively. In the crystals molecules form a sheet-like network perpendicular to the b axis, with short intermolecular S...N distances (3.047 and 3.086 angstrom for 1 and 3.076 angstrom for 2). The internetwork distances between S atoms are significantly shorter than the van der Waals contact: 3.451 and 3.461 angstrom for 1 and 2, respectively. Each molecule has a butterfly shape. Two dicyanomethylene groups are bent from the quinonoid ring to the same side and two thiophene rings are bent to the opposite side of the dicyanomethylene groups.