Ru II and Ir III Complexes Containing ADA and DAD Triple Hydrogen Bonding Motifs: Potential Tectons for the Assembly of Functional Materials

The synthesis and characterisation of a series of [Ru (bpy) L] and [Ir(ppy) L] complexes containing ligands L with the potential to engage in triple hydrogen bonding interactions is described. L1 and L2 comprise pyridyl triazole chelating units with pendant diaminotriazine units, capable of donor-acceptor-donor (DAD) hydrogen bonding, while L3 and L4 contain ADA hydrogen bonding units proximal to N^N and N^O cleating sites, respectively. X-ray crystallography shows the L1 and L2 containing Ru complexes to assemble via hydrogen bonding dimers, while [Ru (bpy) L4] assembles via extended hydrogen bonding motifs to form one dimensional chains. By contrast, the expected hydrogen bonding patterns are not observed for the Ru and Ir complexes of L3. Spectroscopic studies show that the absorption spectra of the complexes result from combinations of MLCT and LLCT transitions. The L1 and L2 complexes of Ir and Ru complexes are emissive in the solid state and it seems likely that hydrogen bonding to complementary species may facilitate tuning of their ILCT emission. Low frequency Raman spectra provide further evidence for ordered interactions in the solid state for the L4 complexes, consistent with the results from X-ray crystallography.