Anamaria D. P. Alexiou

Monomeric and extended oxo-centered triruthenium clusters

Abstract The chemistry of μ-oxo-centered trinuclear ruthenium-carboxylate clusters, of general formula [Ru 3 O(RCO 2 ) 6 L 3 ] n , has been dealt with special emphasis on their spectroscopic and electrochemical properties, as well as their capability to form ligand-bridged oligomeric structures exhibiting pronounced electronic delocalization. Mixed systems containing trinuclear ruthenium clusters attached to transition metal complexes and porphyrins are also focused upon in this review article, from the point of view of cooperative interactions and supramolecular chemistry. The role of the trinuclear clusters as electron donor/acceptor groups, and their relevance in biomimetic systems, redox catalysis and molecular devices have been discussed.

A new highly efficient tetra-electronic catalyst based on a cobalt porphyrin bound to four μ3-oxo-ruthenium acetate clusters

A meso-tetra(4-pyridyl)cobaltporphyrin modified with four [μ3-O-Ru3(Ac)6(py)2]+ clusters (CoTCP=cobalt tetraclusterporphyrin) has been synthesized and characterized by 1H-NMR and UV–Vis spectroscopy, electrochemistry and spectroelectrochemistry. The facility of CoTCP to form adherent and durable films on a glassy carbon surface has been exploited in the preparation of modified electrodes exhibiting outstanding catalytic activity in the tetraelectronic reduction of dioxygen to water. This finding has been confirmed from the linear behavior and the slope of the Levich plots up to 4000 rpm, as well as from the high current densities, e.g. up to 2.8 mA cm−2 obtained for the modified electrodes. The enhanced activity has been interpreted in terms of the electronic activation of the cobalt porphyrin by the peripheral triangular ruthenium cluster complexes, as supported by detailed spectroelectrochemical data confirming a significant electronic coupling between the cobalt porphyrin and [μ3-O-Ru3(Ac)6]+ groups.

Extended Electronic Interactions in a Triangular μ‐Oxotriruthenium Acetate Cluster Containing Nitric Oxide

The binding of NO to the trinuclear cluster [Ru3O(CH3CO2)6(py)2]+ (py = pyridine) leads to a stable, diamagnetic [Ru3O(CH3CO2)6(py)2(NO)]+ complex, displaying extended electronic interactions which arise from the coupling of the unpaired π* electron of NO and the unpaired electron in the π-orbitals of the Ru3O unit. This complex has been isolated and its spectroscopic characterization (EPR, 1H and 13C NMR, IR, UV/Vis) and electrochemical/spectroelectrochemical properties are reported in this paper. The NO0 character in the complex is supported by spectroscopic and electrochemical results, as well as by semi-empirical theoretical calculations carried out for the complex. A remarkable point in this system is the dramatic changes in the Ru−NO electronic interactions accompanying the several successive redox states of the triangular Ru3O center. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Nitric oxide photorelease from a trinuclear ruthenium nitrosyl complex and its in vitro cytotoxicity against melanoma cells

In vitro cytotoxicity study of the [Ru3O(CH3COO)6(4-pic)2(NO)]PF6 triruthenium nitrosyl cluster (compound 1, 4-pic=4-methylpyridine) against B16F10 melanoma cell line was evaluated in the presence and absence of visible light irradiation. The nitrosyl cluster 1 showed a significant tumoricidal activity when irradiated at λ=532 nm, reducing cell viability up to 90% at a concentration of 62.5 μM. However, cell death of 60% is also observed in the dark which can be assigned to the NO release mediated by a redox reaction of the cluster in cell medium. This possibility was confirmed by amperometric detection of NO after the addition of ascorbic acid to compound 1 in phosphate buffer. A control experiment was performed with the solvated cluster [Ru3O(CH3COO)6(4-pic)2(CH3OH)]PF6 (compound 2) and no significant lowering of cell viability was observed. These results suggest that the nitrosyl cluster acts as a pro-drug, delivering NO, which is the actual active species.

Dynamic electrochemical behaviour of a trinuclear μ-oxo ruthenium acetate cluster containing pyridine and dimethylsulphoxide ligands

Abstract The electrochemical and spectroelectrochemical behaviour of the [Ru 3 O(O 2 CCH 3 ) 6 (py) 2 (dmso)] + complex (py = pyridine, dmso = dimethylsulphoxide) is discussed. Four reversible waves were observed around 2.1, 1.2, 0.2 and −0.95 V, corresponding to the successive redox couples Ru IV Ru IV Ru III /…/Ru III Ru II Ru II , respectively. Dramatic spectral changes and splitting of the electrochemical waves around 0.2 V, were ascribed to an intramolecular O-bound to S-bound dmso linkage isomerization reaction. In pure acetonitrile solutions, a parallel dissociation of O-bound dmso is also observed. The evaluation of the kinetic and equilibrium constants for the dissociation and linkage isomerization reactions is reported.

13C NMR spectra of triangular μ-oxoruthenium acetate clusters revisited: HETCOR study of two pyridine and 4,4′-bipyridine derivative

The previous assignment of the 13C NMR spectra of triangular [Ru3O(CH3CO2 )6L3]+ clusters (L=pyridine derivatives) has been revised based on 1H–13C HETCOR and HMBC analysis. ©1999

Propriedades e aplicações de clusters trinucleares de carboxilatos de rutênio

A review with 94 references focusing on m3-oxo-triruthenium carboxylate clusters is presented. The electronic, magnetic, electrochemical, and catalytic properties of these compounds are discussed. Main synthetic routes and structural characteristics, including their use as building blocks in supramolecular systems are described.

A Trinuclear Oxo-Chromium(III) Complex Containing the Natural Flavonoid Primuletin: Synthesis, Characterization, and Antiradical Properties

A new trinuclear oxo-centered chromium(III) complex with formula [Cr3O(CH3CO2)6(L)(H2O)2] (L = 5-hydroxyflavone, known as primuletin) was synthetized and characterized by ESI mass spectrometry, thermogravimetry, and 1H-NMR, UV-Vis, and FTIR spectroscopies. In agreement with the experimental results, DFT calculations indicated that the flavonoid ligand is coordinated to one of the three Cr(III) centers in an O,O-bidentate mode through the 5-hydroxy/4-keto groups. In a comparative study involving the uncoordinated primuletin and its corresponding complex, systematic reactions with the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) showed that antiradical activity increases upon complexation.

Can mass dissociation patterns of transition-metal complexes be predicted from electrochemical data?

The Cooks kinetic method has been very convenient to correlate the relative dissociation rates obtained by collision-induced fragmentation experiments with the energies of two related bonds in molecules and complexes in the gas phase. Reliable bond energy data are, however, not always available, particularly for polynuclear transition-metal complexes, such as the triruthenium acetate clusters of the general formula [Ru(3) (micro(3)-O)(micro-CH(3)COO)(6)(py)(2)(L)](+), where L = ring substituted N-heterocyclic ligands. Accordingly, their gas-phase collision-induced tandem mass spectrometry (CID MS/MS) dissociation patterns have been analyzed pursuing a relationship with the more easily accessible redox potentials (E(1/2)) and Levers E(L) parameters. In fact, excellent linear correlations of ln(1/2A(L)/A(py)), where A(py) and A(L) are the abundance of the fragments retaining the pyridine (py) and L ligand, respectively, with E(1/2) and E(L) were found. This result shows that those electrochemical parameters are correlated with bond energies and can be used in the analysis of the dissociation data. Such modified Cooks method can be used, for example, to determine the electronic effects of substituents on the metal-ligand bonds for a series of transition-metal complexes.

Synthesis of a trinuclear ruthenium cluster containing pyridine and 4-acetylpyridine ligands and its immobilization on functionalized silica

SummaryThe trinuclear cluster [Ru3O(Ac)6(py)2(acpy)]PF6 (py: pyridine;acpy: 4-acetylpyridine) has been synthesized and anchored on functionalized silica. Five successive redox couples exhibitingE°=−1.4, −0.98, 0.21, 1.23, and 2.2 Vvs. SHE have been characterized in acetonitrile solutions based on cyclic voltammetry and spectroelectrochemical measurements. The redox and spectroscopic properties are maintained in the immobilized species, allowing its use in optodes and in electron transfer processes.ZusammenfassungDer dreikernige Cluster [Ru3O(Ac)6(py)2(acpy)]PF6(py: Pyridin;acpy: 4-Acetylpyridin) wurde hergestellt und an funktionalisiertem Kieselgel verankert. Mit Hilfe cyclischer Voltammetrie und spektroelektrochemischer Messungen konnten fünf aufeinanderfolgende Redoxpaare beobachtet werden (E0=−1.4, −0.98, 0.21, 1.23 und 2.2 V bezüglich SHE). Die elektrochemischen und spektroskopischen Eigenschaften bleiben in den fixierten Clustern erhalten und erlauben deren Verwendung in Optoden und bei Elektronenübertragungsprozessen.