Under simulated solar irradiation in the visible spectral region, the catalytically active RuIV-oxo species [Ru(O)(bpy)(tppz)]2+ (tppz = tetrapyridylpyrazine, a strongly π-accepting tridentate N, N, N-ligand) is produced directly from a single metal-to-ligand charge-transfer (MLCT) photoexcitation of the resting RuII-aquo complex [Ru(H2O)(bpy)(tppz)]2+ in aqueous media containing an electron acceptor. This photoinduced path to 2-electron/2-proton activation of a mononuclear catalyst (i.e., without a paired chromophoric unit) is enabled by the thermodynamic instability of the intermediate RuIII-hydroxo species [Ru(OH)(bpy)(tppz)]2+, which promptly disproportionates into the RuIV-oxo and RuII-aquo states as electrochemically observed by cyclic and pulse voltammetries in a wide range of pH. The proton-coupled multielectron photocatalytic capability of the complex in neutral aqueous solutions, at room conditions, was demonstrated through the dehydrogenative oxidation of benzyl alcohol into benzaldehyde with a product selectivity of about 100%. The performance of this mononuclear complex acting as chromophore/catalyst is comparable to that of the previously reported dinuclear complex [(tpy)Ru(tppz)Ru(HxO)(bpy)]4+. In addition to the characterization of redox and spectroscopic properties for the [Ru(L)(bpy)(tppz)]n+ derivatives with L = Cl- or HxO, structural analysis of the precursor chloro complex [RuCl(bpy)(tppz)](PF6) was also performed by single-crystal X-ray diffraction in this work.

This paper provides a survey of general aspects involved in the coordination chemistry of low-valent (mainly +III,+II), low-spin (d p5,d p6) ruthenium ions with ethylenediamine-N,N,N',N'-tetraacetate (edta) and their substituted derivatives. The topics covered herein include structure, reactivity, kinetics, thermodynamics, electrochemistry and spectroscopy. The contributions from either our research group or the literature over the last three decades are focused in this review.

This article reports on some basic and conceptual principles concerning electron transfer (ET) and/or intervalence transfer (IT) phenomena in inorganic mixed-valence systems.

Complexos de ferro e rutênio do tipo [M-LH]n (onde M = RuII,III(NH3)5(2+,3+), RuII,III(edta)2-,- [edta = etilenodinitrilotetraacetato], ou FeII,III(CN)5(3-,2-) e LH = benzotriazol ou benzoimidazol) foram preparados e caracterizados em solução aquosa através de métodos eletroquímicos e espectroeletroquímicos. Neste trabalho, maior ênfase foi direcionada aos processos redox dependentes do pH, que foram demonstrados por todos os complexos estudados. Os valores de pKa e de potencial de redução formal foram obtidos a partir dos diagramas de E1/2 versus pH, que apresentaram comportamento tipicamente Nernstiano. Os diagramas de Pourbaix também foram usados para ilustrar o particionamento entre as espécies redox e os equilíbrios ácido-base envolvidos nas reações. Na avaliação da potencialidade desses complexos como modelos simples para reações de transferência de elétrons acoplada a próton (PCET), considerou-se a extensão da região onde a dependência do par redox M III/M II com o pH é ativa, definida entre pKaIII e pKaII. Os resultados obtidos neste trabalho foram analisados do ponto de vista do caráter eletrônico doador/receptor dos ligantes e das interações sigma,pi-metal-ligante envolvidas em cada espécie, para ambos os estados de oxidação do íon metálico.

Iron and ruthenium complexes of the type [M-LH]n (where M = RuII,III(NH3)5(2+,3+), RuII,III(edta)2-,- [edta = ethylenedinitrilotetraacetate], or FeII,III(CN)5(3-,2-) and LH = benzotriazole or benzimidazole) were prepared and characterized in aqueous solutions by means of electrochemical and spectroelectrochemical methods. Special emphasis was given to the pH-dependent redox processes, exhibited by all the investigated complexes. From their related Pourbaix diagrams, which displayed a typically Nernstian behavior, the pKa and formal reduction potential values were extracted. In addition, these E1/2 versus pH curves were also used to illustrate the partitioning relationship concerning the redox and acid-base species, and their interconversion equilibria. The active area in which the dependence of the M III/M II couple on the pH takes place, as delimited by pKaIII and pKaII, was taken into account in order to evaluate the usefulness of such simple complexes as models for proton-coupled electron transfer (PCET). The results were interpreted in terms of the acceptor/donor electronic character of the ligands and sigma,pi-metal-ligand interactions in both redox states of the metal ion.