Liquid-crystalline coordination polymers based on tetra(alkoxybenzoato)dirhodium(II) complexes axially linked by tetrazine, phenazine and 4,4′-bipyridine

Abstract

The reaction of dirhodium tetrakis(3,4,5-trialkoxy)benzoates Rh₂(B3OCn)₄ (n = 10, 14, and 18) with three different dinitrogenated axial ligands (L_ax), namely tetrazine (tz), phenazine (phz), and 4,4′-bipyridine (bpy), gave rise to three homologous series of mesogenic coordination polymers, [Rh₂(B3OCn)₄]L_ax. All of them exhibited thermotropic columnar mesophases that were of the hexagonal type for tz and phz and rectangular for bpy. The lighter n = 10 homologs of the three series are liquid crystals (LC) at room temperature. Their mesomorphic properties have been compared with those of the previously studied L_ax = pyrazine series. Models for the supramolecular organization of the three polymeric series in their Col LC phases are proposed on the basis of their structural parameters, as measured by XRD and SAXS. The differences are interpreted in terms of different coordination features of the axial ligands.

Keywords:

• Coordination polymers
• nitrogenated axial ligands
• bimetallic carboxylates
• metal-metal bond
• metallomesogens
• columnar mesophases
• structural models

Acknowledgements

FDC, CHI, and MAC are members of the research staff of CONICET. SAXS experiments at INIFTA were performed thanks to project “Nanopymes” (EuropeAid/132184/D/SUP/AR-Contract-896). We thank Dr. P.S. Antonel for allowing us to anticipate some preliminary results of our study on oriented fibers, as well as CONICET for a PhD fellowship to LR.