Crystal Packing of Potentially Mesomorphic Azobenezene Derivatives R-1-C6H4-N=N-C6H4-R-2 (R-1, R-2 = CH3COO, C2H5O; CH2=C(CH3)COO, C2H5; C6H13COO, C2H5O)

Abstract The structure and thermal properties of azobenzene derivatives R 1 –C 6 H 4 –N=N–C 6 H 4 – R 2 , where R 1 / R 2 = CH 3 COO/C 2 H 5 O ( I ), CH 2 =C(CH 3 )COO/C 2 H 5 ( II ), or C 6 H 13 COO/C 2 H 5 O ( III ), were studied by differential scanning calorimetry and X-ray diffraction. Compounds I and III form a mesophase (nematic) upon melting, whereas compound II does not produce a mesophase. Compound III is characterized by two high-temperature crystal–crystal phase transitions III III – III II – III I . The low-temperature crystal modification, which is not a precursor of the mesophase, was structurally characterized. The crystal packing of I is stabilized by C−H···π interactions and consists of alternating loosely and closely packed regions. Weak directional interactions that connect the molecules into zigzag chains ensure the structuring of the mesophase of I . The possible structuring pattern of the mesophase of III is discussed.