Does geometry matter? Effect of the ligand position in bimetallic ruthenium polypyridine siblings

Abstract

The properties of trans-[RuII(tpy)(bpy)(μ-CN)RuIII(py)4(L)]3+/4+ (L = Cl−, NCS−, DMAP or MeCN) show a transition from localized to delocalized as the ΔE between Ru ions becomes smaller.

A Strongly Coupled Biruthenium Complex as Catalyst for the Water Oxidation Reaction

“…The latter is an intervalence charge transfer (IVCT) band as expected for a mixed-valence complex, while the disappearance of the band at 28100 cm À 1 confirms that the oxidation is centred in the {Ru(py) 4 } moiety. As observed previously, [8] the MLCT band centred at the {Ru(tpy)(bpy)} fragment shifts to higher energies (Table 1) due to the influence of the Ru(III) moiety attached to the cyanide bridge. At pH 7 the oxidation by one electron also results in the disappearance of the band at 28100 cm À 1 , but in this case the IVCT band appears at 14600 cm À 1 .…”

“…The complex [Ru(tpy)(bpy)(μ-CN)Ru(py) 4 (OH 2 )] 3 + (Ru II Ru II OH 2 , Scheme 1) was prepared by a slight modification of the reported procedure [8] involving the reaction of nitrosyl complex with azide under argon in aqueous solution (see Supporting Information for details).…”

“…The visible spectrum of Ru II Ru II OH 2 is identical at both pHs and is dominated by two sets of metal-to-ligand charge transfer (MLCT) transitions (Figure 3 and Table 2) from both Ru centres to the aromatic ligands as observed for other complexes of the [Ru(tpy)(bpy)(μ-CN)Ru(py) 4 L] 3 + family. [8] The more intense transition at 28100 cm À 1 corresponds to the {Ru(py) 4 } fragment, while the weaker band shifted to the red at 23000-22000 cm À 1 is associated with the {Ru(tpy)(bpy)} chromophore (Figure 3).…”

“…(TD)DFT calculations (TD)DFT calculations have shown to be a very useful tool to understand the spectroscopy of RuÀ Ru cyanide bridged complexes in different oxidation states. [8][9][10]14,15] Figure 4 shows that (TD)DFT calculations indicate that the unpaired electron in complex Ru II Ru III OH 2 is substantially delocalized between both Ru ions through the interaction promoted by the cyanide bridge (Figure S4). As observed for related mixed-valence cyanide-bridged diruthenium polypyridines the calculated energy for the IVCT transition is lower than the observed one, which is indicative of a DFT overestimation of the delocalization compared to the experimental one.…”

“…Cyanide bridge is among the most explored bridges in the literature, and it can promote a strong coupling demonstrated by its ability to promote charge delocalization in diruthenium mixed-valence complexes. [8][9][10][11] In this work, we show that the strongly coupled biruthenium complex trans-[Ru(tpy)(bpy)(μ-CN)Ru(py) 4 (OH 2 )] 3 + (Ru II Ru II OH 2 , where tpy = 2,2':6',2''-terpyridine, bpy = 2,2'-bipyridine and py = pyridine) can also act as an active water oxidation catalyst for the reaction with an excess of Ce(IV) at pH 1. The rate determining step of the reaction is first order both in Ce(IV) and Ru II Ru II OH 2 and we assign the resting state of the catalytic cycle as the three-electron oxidized complex trans-[Ru III (tpy)(bpy)(μ-CN)Ru IV (py) 4 =O] 3 + (Ru III Ru IV =O).…”