Publications

Lipophilic paddle-wheel biruthenium complexes [Ru2(μ-O2CR)3X]n (O2CR = 3,4,5-tridodecyloxybenzoate, X = Cl, I) self-assemble in organic media to form halogen-bridged coordination polymers. The polymerization is accompanied by spectral changes in π(RuO,Ru2) → π*(Ru2) and π(axial ligand) → π*(Ru2) absorption bands. These polymeric complexes form lyotropic liquid crystals in n-decane at concentrations ≳100 unit mM. The bridging halogen axial ligands (X = Cl or I) exert significant influences on their electronic structures and self-assembling characteristics: the chloride-bridged polymers give hexagonally aligned ordered columnar structure (columnar hexagonal phase, Colh), whereas the iodide-bridged polymers form less ordered columnar nematic (Coln) phase, as revealed by small-angle x-ray diffraction measurements. Chloro-bridged coordination polymers dispersed in n-decane are thermally intact even at the elevated temperature of 70°. In contrast, iodo-bridged polymers show reversible dissociation and reassembly phenomena depending on temperature These halogen-bridged coordination polymers show unidirectional alignment upon applying a.c. elec. field as studied by crossed polarizing optical microscopy and SEM. The unidirectionally oriented columns of chloro-bridged polymers are accumulated upon repetitive application of the a.c. voltage, whereas iodo-bridged coordination polymers show faster and reversible alignment changes in response to turning on-and-off the elec. field. The controlled self-assembly of electronically conjugated linear complexes provide a potential platform to design elec. field-responsive nanomaterials.