An Isomeric Series of Thiophene-Fused Tetracyanoquinodimethanes. II. The Crystal and Molecular Structures

Abstract

Abstract The crystal structures of three isomeric thiophene-fused TCNQs, 4,8-bis(dicyanomethylene)-4,8-dihydrobenzo[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 P21/n. For 1, a = 16.588(3), b = 7.222(5), c = 11.353(3) Å, β = 89.88(2)°, V = 1360.1(10) Å3, Z = 4, Dx = 1.545 Mg m−3. For 2a = 16.594(4), b = 7.232(2), c = 11.433(2) Å, β = 91.05(2)°, V = 1371.8(5) Å3, Dx = 1.532 Mg m−3. For 3a = 16.738(2), b = 7.342(3), c = 10.922(3) Å, β = 92.98(2)°, V = 1340.4(7) Å3, Dx = 1.568 Mg m−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 Å for 1 and 3.076 Å for 2). The internetwork distances between S atoms are significantly shorter than the van der Waals contact: 3.451 and 3.461 Å 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.