H-Bonded metallomesogens derived from salicyladiminates

A series of new mesogenic compounds 1a-b (n=8, 10, 12, 14, 16) derived from salicyladimines and their palladium 2a, 2b, vanadyl 2a, and copper complexes 3a, 3b were prepared and their mesomorphic properties investigated by optical microscopy, differential scanning calorimetry and powder X-ray diffractornetry. Pd(2+) and VO(2+) ions formed mononuclear complexes, whereas, Cu(2+) ion formed binuclear complexes due to the relative acidic strength of Schiff base. Single crystallographic analysis of non-mesogenic compound 2a (n=8) confirmed its coordination geometry at Pd(2+) as square plane. It crystallizes in a triclinic space group P-1 with a Z=1. As expected, the Pd(2+) was coordinated via a trans-N(2)O(2) donor set of phenolic-O and imine-N atoms, leaving two hydroxyl groups intact and uncoordinated. The two alkoxy chains, pointing to the opposite direction were parallel, and the molecule was considered as twisted Z-shaped. Both hydroxyl-OH groups attached on C(17) and C(18)-Schiff imines participate in the H-bonds in the lattice. Interestingly, a pseudo polymeric structure was observed, in which H-bonded dimer was continuously extended by another H-bonded dimer in the lattice. Compounds 1 exhibited smectic A phases, and Pd and VO complexes and Cu complexes 3b exhibited smectic A or/and smectic X phases, however, Cu complexes 3a formed crystal phases. Intermolecular H-bonds might be attributed to the difference observed on the mesomorphic properties in these compounds. Copper complexes 2b were not active on ESR spectroscopy. (c) 2010 Elsevier Ltd. All rights reserved.