(Polypyridyl)ruthenium(II) Complexes Based on a Back‐to‐Back Bis(pyrazolylpyridine) Bridging Ligand

Two (polypyridyl)ruthenium(II) complexes, [(tpy)Ru II (L)](PF 6 ) 2 ( 1 ) and [(tpy)Ru II (L)Ru II (tpy)](PF 6 ) 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 1 H and 13 C 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 Ru II 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.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)