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Controlling the local concentration of metal complexes at the surface of ionic liquids (ILs) is a highly sought‐after objective due to its pivotal implications in supported ionic liquid phase (SILP) catalysis. Equally important is to avoid per‐ and polyfluorinated substances due to environmental concerns. Herein, we investigate the surface enrichment of Ru polypyridyl complexes with fluorine‐free alkylic side groups of varying lengths and shapes, using the hydrophilic IL [C2C1Im][OAc] as solvent. Additional charged carboxylate groups are included into the polypyridyl ligands to increase the solubility of the complex in the IL. When the ligand system is functionalized with long and hydrophobic alkyl side chains, the complex predominantly localizes at the IL/vacuum interface, as deduced from angle‐resolved X‐ray photoelectron spectroscopy. Conversely, in the presence of short or more bulky substituents, no surface enrichment is observed. This buoy‐like behaviour with fluorine‐free side groups is explored for 0.05 %mol to 1 %mol solutions. Intriguingly, surface saturation occurs at approximately 0.5 %mol, which is beneficial to the efficient operation of catalytic systems featuring high surface areas, such as SILP catalysts. [ABSTRACT FROM AUTHOR]

The catalytic activity towards water oxidation of a strongly coupled bimetallic ruthenium complex, trans‐[Ru(tpy)(bpy)(μ‐CN)Ru(py)4(OH2)]3+ (RuIIRuIIOH2), where tpy=2,2′:6′,2"‐terpyridine, bpy=2,2′‐bipyridine and py=pyridine are presented. At pH 1 the first two oxidation reactions are centred at the aquo fragment and result in the RuIIRuIIIOH2 and RuIIRuIVO redox states as confirmed by its spectroscopy and DFT calculations. Oxidation by an additional electron is followed by an irreversible step and a catalytic wave associated with the water oxidation reaction. At pH 1 the reaction with an excess of Ce(IV) results in the generation of an stoichiometric amount of oxygen based on molar amounts of the added Ce(IV). The dominant species during the catalytic cycle is the three‐electron oxidized product, RuIIIRuIVO. The reduction of the concentration of Ce(IV) monitored at 370 nm follow the rate equation, −d[Ce(IV)]/dt=kox[Ce(IV)][RuIIRuIIOH2] with a kox=82±3 M−1s−1 at T=298 K. The RuIIIRuIVO species is not stable and reacts to give RuIIRuIVO. [ABSTRACT FROM AUTHOR]

The cover feature shows a ruthenium(II) polypyridine complex dissolved in 1‐ethyl‐3‐methylimidazolium acetate under X‐ray irradiation. The long hydrophobic alkyl chains of the complex act as buoys, pulling it towards the liquid/vacuum interface, as proven by ARXPS measurements. More details can be found in the Research Article by Hans‐Peter Steinrück, Federico J. Williams, and co‐workers (DOI: 10.1002/open.202400092)...By Luciano Sanchez Merlinsky; Daniel Hemmeter; Luis M. Baraldo; Florian Maier; Hans‐Peter Steinrück and Federico J. WilliamsReported by Author; Author; Author; Author; Author; Author [Extracted from the article]

In this work, we present the preparation of a complex [(tpy)(bpy)Ru(μ-CN)Ru(py)4(OH2)](PF6)3 (tpy = 2,2′,6′,2′′-terpyridine; bpy = 2,2′-bipyridine; py = pyridine) that combines a ruthenium chromophore linked to another ruthenium ion that bears a labile position trans to the bridge. Substitution in this position is very attractive, as it allows us to place a quencher trans to the chromophore maximizing the separation between them. This complex allowed us to prepare a family of cyanide-bridged ruthenium polypyridines of general formula [Ru(tpy)(bpy)(μ-CN)Ru(py)4(L)]2/3+ (L = Cl−, NCS−, 4-dimethylaminopyridine or acetonitrile) and compare them with the related complexes [Ru(tpy)(bpy)(μ-CN)Ru(bpy)2(L)]2/3+ where the L ligand lies cis to the bridge. The mixed-valence form of these complexes shows evidence of strong coupling between the ruthenium ions and enhanced delocalization as the redox potential of the {Ru(py)4L} fragment increases. (TD)DFT calculations reproduce very well the experimental spectra of these complexes and indicate that when L = acetonitrile, the hole in the mixed-valence complex is almost equally distributed between both ruthenium ions. For L = DMAP and NCS− the π orbitals of the ligands are mixed with dπ orbitals of the Ru ions, resulting in partial delocalization of the charge on the ligands. The latter result illustrates that the trans configuration of these complexes is well-suited to extend the interaction beyond the bridged ruthenium ions. [ABSTRACT FROM AUTHOR]

In this work, we report the evolution of the properties of the inter-valence charge transfer (IVCT) transition in a family of cyanide-bridged ruthenium polypyridines of general formula [RuII(tpy)(bpy)(μ-CN)RuIII(bpy)2(L)]3/4+ (tpy = 2,2′,6′,2′′-terpyridine; bpy = 2,2′-bipyridine; L = Cl−, NCS−, 4-dimethylaminopyridine or acetonitrile). In these complexes, the redox potential difference between both ruthenium centers (ΔE) is systematically modified. A decrease in ΔE causes a red shift of the energy and an intensity enhancement of the observed IVCT transitions. For L = acetonitrile, the IVCT band becomes narrower and asymmetrical, and shows very little dependence on the nature of the solvent, suggesting a delocalized configuration, although a non-symmetrical one. Also, additional electronic transitions of low energy are clearly resolved in this complex. The observed variation in the properties of the IVCT transitions can be understood on the basis of DFT calculations, that point to increasing mixing between the dπ orbitals of both Ru ions. [ABSTRACT FROM AUTHOR]

Ligand field (LF) states have been present in discussions on the photophysics and photochemistry of ruthenium-iminic chromophores for decades, although there is very little documented direct evidence of them. We studied the picosecond transient absorption (TA) spectroscopy of four {RuII(imine)} complexes that respond to the formula trans-[Ru(L)4(X)2], where L is either pyridine (py) or 4-methoxypyridine (MeOpy) and X is either cyanide or thiocyanate. Dicyano compounds behave as most ruthenium polypyridines and their LF states remain silent. In contrast, in the dithiocyanate complexes we found clear spectroscopic evidence of the participation of LF states in the MLCT decay pathway. These states are of donor and acceptor character simultaneously and this is manifested in the presence of MLCT and LMCT transient absorption bands of similar energy. Spectroelectrochemical techniques supported the interpretation of the absorption features of MLCT states, and DFT methods helped to assign their spectroscopic signatures and provided strong evidence on the nature of LF states. [ABSTRACT FROM AUTHOR]

The NIR and IR spectroscopic properties of the cyanide-bridged complex, trans-[Ru(dmap)4{(μ-CN)Ru(py)4Cl}2]3+ (py=pyridine, dmap=4-dimethylaminopyridine) provide strong evidence that this trimetallic ion behaves as a Class III mixed-valence species, the first example reported of a cyanide-bridged system. This has been accomplished by tuning the energy of the fragments in the trimetallic complex to compensate for the intrinsic asymmetry of the cyanide bridge. Moreover, (TD)DFT calculations accurately predict the spectra of the trans-[Ru(dmap)4{(μ-CN)Ru(py)4Cl}2]3+ ion and confirms its delocalized nature. [ABSTRACT FROM AUTHOR]

The NIR donor-acceptor charge transfer (DACT) bands of the series of trinuclear complexes trans-[(NC)5FeII/III-(μ-CN)RuIIL4μ-NC)FeIII(CN)5]5/4- (L= pyridine, 4-tert-butylpyridine, and 4-methoxypyridine) are analyzed in terms of a simplified molecular orbital picture that reflects the interaction between the donor and acceptor fragments. The degree of electronic coupling between the fragments is estimated by a full fit of the DACT band profiles according to a three-state model inspired in the Mulliken-Hush formalism. The information is complemented with determinations performed on the asymmetric heterotrinuclear species trans-[(NC)5CoIII(μ-CN)RuII(py)4(μ-NC)FeIII(CN)5]4-, whose preparation is reported here for the first time. The analysis of the NIR spectra of the symmetric trans-[(NC)5FeIII-(μ-CN)RuIIL4(μ-NC)FeIII(CN)5]4- species reveals a low degree of mixing between the terminal acceptor fragments and the bridging moiety containing RuII, with H12 values between 1.0 × 10³ and 1.5 × 10³ cm-1. The reorganization energy contributions seem to be the same for the three species, even when the spectra were recorded in different media. This observation also applies for the CoIII-substituted compound. The computed potential energy surfaces (PES) of the ground state for these complexes show only one stationary point, suggesting that the FeII-RuIII-FeIII (or FeII-RuIII-CoIII) electronic isomers are not thermally accessible. One-electron reduction leads to asymmetric trans-[(NC)5FeII(μ-CN)RuIIL4(μ-NC)FeIII(CN)5]5- compounds with potentially two DACT bands involving the RuII and the FeII donor fragments. These species reveal a similar degree of electronic mixing but the PES shows three minima. We explore the role of the bridging fragment in the long-range thermally induced electron transfer between the distant iron centers. The results suggest that superexchange and hopping might become competitive paths, depending on the substituents in the bridging fragment. [ABSTRACT FROM AUTHOR]

In this article, we report the structural, spectroscopic, and electrochemical properties of the cyanide-bridged complex salts trans-[(NC)RuII(L)4(μ-CN)RuII(py)4Cl]PF6 and trans-[RuIIL)4{(μ-CN)-RuII(py)4Cl}2] (PF6)2 (L = pyridine or 4-methoxypyridine). The mixed-valence forms of these compounds show a variety of metal-to-metal charge-transfer bands, including one arising from charge transfer between the remote ruthenium units. The latter is more intense when L = 4-methoxypyridine and points to the role of the bridging ruthenium unit in promoting mixing between the du orbitals of the terminal fragments. [ABSTRACT FROM AUTHOR]