High-molecular-weight ruthenium(II) coordination polymers: Synthesis and solution properties

A synthetic strategy is presented that allows the preparation of high-molecular-weight ruthenium(II) coordination polymers 1a, b of homogeneous molecular constitution. The key to this success was the development of an efficient procedure leading to highly pure ''metal monomers'' [Ru(R(2)bpy)Cl-3](x) (3a, b) with (b: R = C6H5) and without (a: R = H) lateral phenyl substituents. Their conversion with equimolar quantities of ''ligand monomer'' tetrapyrido[3, 2-a:2', 3'-c:3'', 2''-h:2''',3'''2j]phenazine (2) gave excellently soluble ruthenium(II) coordination polymers 1a and 1b, respectively, the molecular constitution of which was proven with high-resolution H-1 and C-13 NMR spectroscopy. The degrees of polymerization were estimated to be P-n greater than or equal to 30 because of the complete lack of end group absorptions in the NMR spectra. This estimate could be verified by small-angle X-ray scattering (SAXS) for the phenyl-substituted polymer 1b: according to these investigations, the molecular weight reaches M-W approximate to 47 000, and the radius of gyration was found to be R-G = 8.4 nm. The intrinsic viscosities of high-molecular-weight polymers 1a and 1b were found to be [eta] x 12 mL.g(-1) for both polymers (0.01 M NaCl/DMA). At low ionic strengths, on the other hand, the unsubstituted polymer 1a displays a much more pronounced polyelectrolyte effect in solvents like ethanol/water than the phenyl-substituted polymer 1b of similar P-n. Considering all these results, the surprisingly high solubility of the conformationally rigid, ribbonlike polyelectrolytes 1a and 1b can be considered to be the result of (i) the coiled shape of the polymers, (ii) the intermolecular Coulomb repulsion and, in the case of the phenyl-substituted polymer 1b, (iii) the laterally-attached phenyl substituents.