Mesomorphic Properties of a Long-Chain Tetraphenylporphyrin Oxomolybdenum (V) : Complex. Effect of the Axial Ligands on the Mesomorphic Properties.

Abstract

The thermal behaviour of new alkyltetraphenylporphyrin oxomolybdenum(V) discotic liquid crystals was studied by DSC, optical microscopy, variable temperature FT-IR and X-ray diffraction. All these complexes, C_<12>TPPMo(O)X (X = OH, OCH_3 and OC_2H_5) exhibited lamellar-type mesophases. Their thermal stability is strongly dependent on the nature of the axial ligand. In the case of the hydroxocomplex, a polymeric stacking of molecules due to an intermolecular hydrogen bond is proposed to exist in the mesophase. The mesomorphic properties of these complexes were compared with those of others tetraphenylporphyrin metallomesogens with axial ligands to explain the differences of thermal behaviour in terms of different molecular interactions between axial groups. The μ-oxodimer, [C_<12>TPPMo(O)]_2O, has also been studied.