Calamitic metallomesogens derived from unsymmetric pyrazoles

Three series of copper(II) complexes 1a-1c derived from unsymmetric pyrazoles 2a-2c were prepared and their mesomorphic properties investigated. The mesomorphic behavior of compounds was studied by differential scanning calorimetry, polarizing optical microscopy, and powder X-ray diffractometry. The crystal and molecular structures of mesogenic copper complex (2a; n=10) of 3-[4-decyloxyphenyl]-1H-pyrazole were determined by means of X-ray structural analysis. It crystallizes in the triclinic space group p-1, with a=4.0890(1) angstrom, b=18.0167(2) angstrom, c=25.5015(5) angstrom, and Z=2. The geometry at copper center was not perfectly square planar. A weak intermolecular H-bond (d=2.36 angstrom) between Cl1 and H2 atoms and pi-pi interaction (ca. 3.45-3.55 angstrom) was also observed. All their precursors 2a-2c were not mesogenic. In contrast. copper complexes 1a formed nematic or smectic C phases and complexes 1b-1c formed crystalline phases. Powder X-ray diffraction experiments confirmed the presence of SmC phase. (C) 2009 Elsevier Ltd. All rights reserved.