Crystal structures of 4-cyano-4-hexylbiphenyl (6CB) and 4-cyano-4-heptylbiphenyl (7CB) in relation to odd-even effects

Crystal structures of 4-cyano-4-hexylbiphenyl (6CB) and 4-cyano-4-heptylbiphenyl (7CB) with low melting points (13.5 and 30 C, respectively) have been determined at 73 and 33 C, respectively, and compared with previously reported structures of other homologues (n = 2-5, 8-11). In the crystal of 7CB, chains and cores stack alternately, where core regions are largely overlapped with distances of 3.575(2) and 3.597(2)A for N (in CN)... C (in phenyl), showing almost the same packing mode as those of 9CB and 11CB. In the crystal of 6CB, CN groups are antiparallel between neighbouring molecules though the interatomic distances are much longer N... C, 3.673(3) and 3.563(3)A than in 8CB and 10CB (3.28-3.43A), resulting in a quite different packing mode from those of 8CB and 10CB, which had been found to be similar, with CN-CN interactions. Systematic comparison of the homologous series (n = 2-11) reveals odd-even effects, CN-phenyl and CN-CN interactions for odd and even members, respectively, in the crystal stru...