The synthesis and mesomorphic properties of unsymmetrical five-ring bent-core compounds containing a fluorine substituent in one of the arms are reported. A comparison of the properties with the symmetrical compounds having two fluorine substituents indicates that the position of this substituent has an influence on the nature of the mesophase observed. Evidence for the occurrence of a transition from the rectangular columnar (B₁) phase to an antiferroelectric lamellar (B₂) phase, which is rather rare, is provided. The mesophases have been characterized using polarized light microscopy, differential scanning calorimetry, X-ray diffraction and electro-optical studies.