The crystal and molecular structures of the homologous mesogenic compounds N-(4-n-pentyloxybenzylidene)-4'-heptylaniline (50.7) and N-(4-n-nonyloxybenzylidene)-4'-butylaniline (90.4) have been determined at room temperature, the starting model obtained by direct methods. The crystals of both compounds belong to the triclinic system with space group P -1: a = 5,645(3), b = 18.92(1), c = 21.85(1) Angstrom, alpha = 80.07(3), beta = 85.95(4), gamma = 84.63(4)degrees with four molecules per unit cell for 50.7 and a = 5.570(2), b = 8.227(4), c = 26.614(12) Angstrom, alpha = 88.40(3), beta = 87.84(3), gamma = 74.66(4)degrees with two molecules per unit cell for 90.4. The structures were refined by full-matrix least-squares calculations to R = 0.061 for 1792 unique observed reflections for 50.7 and to R = 0.074 for 983 unique reflections for 90.4. The conformations of 50.7 and 90.4 differ considerably from each other. In the two crystallographically independent molecules of 50.7 the phenyl rings of one mesogenic group are twisted by 58.0 degrees and 56.1 degrees, respectively. In contrast to these conformations. in 90.4 they are nearly coplanar. The molecular packing in 90.4 and 50.7 differs as well. 90.4 shows a tilted smectic-like layer structure. The structure of 50.7 consists of blocks, in which the mesogenic units overlap almost completely. These blocks are arranged in a stepwise shifted fashion. But both compounds transform to a smectic C phase at higher temperature.