(Polypyridyl)ruthenium(II) Complexes Based on a Back‐to‐Back Bis(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.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Terpyridine and 2,6-di(1H-pyrazol-1-yl)pyridine substituted cyclotri- and polyphosphazene ruthenium(II) complexes: Chemical and physical behaviour

“…The ruthenium-bpp-terpy complexes (5, 10, 11 and 12) exhibit a different behaviour (see Fig. 7) with a MLCT band in the range 432-440 nm, similar to the few available literature examples [14,21]. They also have a second band at 350-380 nm which is more pronounced for 11 and 12 than 5 and 10.…”

“…Compared to the reported values of the complexes studied by Ruben et al [21], these high oxidation potentials are likely due to the electron-withdrawing effects of the phosphazene ether unit.…”

“…They have a broad absorbance with no clearly defined peaks suggesting a difference in coordination behaviour. Previously, Ruben et al [21] reported that it was necessary to remove a chloride from the ruthenium trichloride complex prior to reacting it with the bpp in order to produce a clean product. This was not necessary for the synthesis of the small molecule complexes as the reactions were performed in neat methanol; however, the polymer reactions were performed in a solution of methanol and THF (50:50).…”

“…The behaviour occurs because Ru(bpp)Cl 3 type complexes are relatively inert when compared to their terpy analogues. In the few available literature reports chloride is removed through the use of a silver salt or high temperature solvents are required to produce Ru(bpp)(terpy) based complexes starting with the Ru(bpp)Cl 3 based precursor [14,21]. If such reaction conditions were used for these ligands a breakdown of the phosphazene would occur, [1] thereby preventing that avenue of enquiry.…”

Two novel cadmium(II) coordination polymers based on bis-functionalized ligand 4′-(4-carboxyphenyl)-2, 2′:6′, 2″-terpyridine

“…In mixed-ligand compound 2, different ligands involve different absorption energies from the same initial metal-based orbital. The emission spectra of compound 2 exhibit a higher energetic MLCT band towards (ox) 2− (around 468 nm) and a lower MLCT band towards (cptpy) − (around 519 nm) in accordance with literature values [21]. The enhancement of luminescence in 1 relative to 2 may be attributed to the ligation of the ligand to the metal center, which more effectively increases the rigidity and reduces the loss of energy by radiationless decay [16,22].…”