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'-heptylb iphenyl (7CB) with low melting points (13.5 and 30 degrees C, respectively) have been determined at -73 and -33 degrees 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) Angstrom fo r 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) Angstrom-than in 8CB and 10CB (3.28-3.43 Angst rom), resulting in a quite different packing mode from those of 8CB and 10C B, 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 t he crystal structures, except for 5CB and 6CB.