Heteroleptic ruthenium(ii) chromophores based on tunable polytopic 4'-(benzamidinato)-2,2':6',2''-terpyridines

A modulable and simple approach towards heteroleptic ruthenium(ii) complexes of amidine-based polypyridine ligands is presented. New complexes 1 and 2 ([(terpyridine)Ru(terpyridine-C₆H₄-C(NR)(NHR))]²⁺ with R = propyl and R = phenyl derivatives, respectively) were characterized by NMR spectroscopy in solution and by X-ray diffraction, which confirmed the obtention of the (E) stereoisomer alone. Depending on the bulkiness of the R-substituents introduced on the amidine moiety, rotational isomerism around the C-N bond could be observed at r.t. Spectroscopic and electrochemical studies showed that the nature of the R-substituents introduced on the amidine moiety can significantly influence the redox and ground-state acido-basic properties of the complexes, while maintaining their electronic features. This particular tunability of polytopic 4'-(amidinato)-terpyridines offers an interesting perspective for photoactive units in larger multi-functional arrays.