Heterobimetallic Ru-Os complexes function as multichannel sensors for selected anions by taking profit of metal-ligand interaction

Heterobimetallic Ru-Os complexes can detect and discriminate cyanide and thiocyanide ions in water through multiple optical channels. [Display omitted] •A new series of Ru-Os complexes were utilized in this work for recognition of selected anions in both organic and aqueous medium.•Imidazole NH protons in the complexes interact with anions either through hydrogen bonding interaction or by complete proton transfer.•The dyads offer multiple optical channels compared with their organic counterparts to visualize the anion recognition events.•The complexes exhibit very high selectivity and sensitivity towards CN− and SCN− in water with very low detection limit up to 10−8 M. In this work we report detailed anion sensing behaviors of a new series of bimetallic Ru(II)-Os(II) complexes derived from an asymmetric heteroditopic bridging ligand (tpy-Hbzim-dipy) consisting of both bipyridine and terpyridine chelating sites covalently connected through phenyl-imidazole spacer. The sensing studies were performed in both organic as well as aqueous medium through multiple optical channels and spectroscopic tools by taking profit of metal ligand interaction in the complexes. The dyads behave as chromogenic and fluorogenic sensors for F−, CN−, AcO− and H2PO4− in acetonitrile without much selectivity. On the other hand, all the four dyads behave as sensors for CN−, SCN−, and S2− in water. Equilibrium/binding constants of the interaction process and detection limits of the complexes towards selected anions were determined from absorption and emission titration data and the values were found to lie in order of 106 M−1 and 10−9 M, respectively. Luminescence lifetimes of the dyads were also modulated to a significant extent by selected anions which in turn justify the utility of the complexes as suitable lifetime-based sensors for selected anions. Finally, test strips were also fabricated based on the metalloreceptors for their probable use as efficient test kits to detect CN−, SCN−, and S2− in pure water for field measurements that do not require any equipment.