Molecular shape has a dominant influence on the existence of the liquid crystalline state. Accurate geometric parameters of a molecule can be determined by X-ray analysis for the crystalline state. Suitable single crystals of 14 mesogenic compounds have been obtained by a huge number of attempts of crystallization from solution. Precise lattice parameters and intensity data have been measured by an automatic four-circle diffractometer (Stoe STADI4, MoKα radiation) at room and low temperature (200 or 220 K). The molecular and crystal structures of these compounds are characterised by geometric parameters (bond lengths and angles, torsion angles) based on complete structure analyses. The compounds have been classified into two groups, 11 molecules with large lateral substituents and 3 "banana-shaped" ones. The molecular structures of the first group show a parallel orientation of the substituent with respect to the basic mesogen. The three homologues of 4,6-dichloro-1,3-phenylene bis[4-(4-n-alkyloxy-phenyleniminomethyl)benzoates] - "banana-shaped" mesogens - exhibit bent angles of about 160° resulting in a considerable approximation to the rod-like shape. Considering the crystal structures, a great variety of molecular packing arrangements has been observed in spite of the chemical similarity of the compounds within both groups. The structural investigations were completed by calculations of isostructurality and packing density.