(Polypyridyl)ruthenium(II) Complexes Based on aBack-to-BackBis(pyrazolylpyridine) Bridging Ligand

Abstract

Two (polypyridyl)ruthenium(II) complexes, [(tpy)RuII(L)](PF6)2 (1) and [(tpy)RuII(L)RuII(tpy)](PF6)4 (2) {tpy is 2,2′:6′,2″‐terpyridine and L is 1,4‐bis[(2,6‐dipyrazol‐1‐yl)pyrid‐4‐yl]benzene}, were synthesised and studied in view of their electrochemical and photophysical properties. The structural characterisation of 1 and 2 was carried out by 1H and 13C NMR spectroscopy, MALDI‐TOF/ESI mass spectrometry and single‐crystal X‐ray analysis. The spectro‐ and electrochemical consequences of the introduction of 2,6‐dipyrazol‐1‐ylpyridine coordinating units into RuII polypyridyl complexes were investigated by UV/Vis, low‐temperature emission spectroscopy and square‐wave voltammetry. It was shown that ligand L can be used as a back‐to‐back bridging ligand in the construction of multinuclear ruthenium(II) ion arrays. In comparison to the widely used 2,2′:6′,2″‐terpyridyl system, the 2,6‐dipyrazol‐1‐ylpyrid‐4‐yl unit was found to act as a relatively strong σ‐donor and weak π‐acceptor ligand which allows its use as a structural and electronic alternative in multinuclear architectures.