1,720,993 research outputs found
Dinuclear Tris(1-pyrazolyl)methane Complexes of Ru(II)
No full textBy exploiting the "complexes-as-metals/complexes-as-ligands" synthetic strategy, six new dinuclear achiral complexes of Ru(II), containing the tripodal ligand tris(1-pyrazolyl) methane (tpm), a chelating ligand (L-L) such as 2,2'-bipyridine (2,2'-bpy), 1,10-phenanthroline (phen) or 2,2'-biquinoline (biq), and either pyrazine (pz) or 4,4'-bipyridine (4,4'-bpy) as bridging ligands (BL), have been prepared and fully characterized. The starting building blocks, many of which have been synthesized for the first time, have been conveniently prepared by improved literature methods. The reactivity of these building blocks in specific experimental conditions has been rationalized. All novel compounds have been characterized fully by elemental analysis and FT-IR. (1)H NMR spectra have been carefully assigned and interpreted on the basis of possible inductive and magnetic anisotropic effects exerted by the ligands. Electrochemical, UV/Vis spectroscopic, and luminescence studies have been carried out on all the dinuclear complexes and their precursor species; the collected data have been discussed and thoroughly interpreted. Ru(II)/Ru(III) mixed-valence species of two dinuclear compounds have been investigated by spectroelectrochemistry and assigned to the Robin and Day's Class II group on the basis of the experimental parameters obtained
Synthesis and Properties of Achiral Asymmetric Dinuclear Tris(1-pyrazolyl)methane Complexes of Ru(II).
No full textExploiting the “complexes-as-metals/complexes-as-ligands” synthetic strategy [1] a family of six novel polypyridyl dinuclear species containing two different Ru tpm)(CL) units [tpm = tris(1-
pyrazolyl)methane, CL = 2,2’-bipyridine, 1,10-phenanthroline, 2,2’-biquinoline] bridged either by
4,4’-bipyridine or pyrazine (see the chart) have been prepared as hexafluorophosphate salts.
These compounds re-present the asymmetric analogues of six dinuclear complexes whose
synthesis and properties have been recently published. Notably, owing to the presence of a tripodal ligand, the metal centres are not chiral, thus the samples are not diastereomeric mixtures, a feature that prevents the structural characterization of oligonuclear trischelate complexes.
All novel complexes have been
thoroughly characterized by elemental analyses and IR spectroscopy, and their 1H
NMR spectra completely assigned on the basis of COSY and NOESY experiments.
The photophysical, electrochemical,
and spectroelectrochemical properties of the new species have also been studied
Mechanistic Insights into Light-Activated Catalysis for Water Oxidation
No full texthe development of catalysts for water oxidation to oxygen has been the subject of intense investigation in the last decade. In parallel to the search for high catalytic performance, many works have focused on the mechanistic analysis of the process. In this perspective, the oxidation of water through light-assisted cycles composed of an electron acceptor (EA), a photosensitizer (PS), and a water oxidation catalyst (WOC) can provide insightful and complementary information with respect to the use of chemical oxidants or to electrochemical techniques. In this minireview, we discuss the mechanistic aspects of the EA/PS/WOC photoactivated cycles, and in particular: (i) the general elementary steps; (ii) the required features and the nature of the PS employed; (iii) the electron transfer processes and kinetics from the WOC to PS+ (hole scavenging); (iv) the detrimental quenching of the PS by the WOC and the alterna-tive mechanistic routes; (v) the identification of WOC intermedi-ates and, finally, (vi) the transposition of the above processes into a dye-sensitized photoanode embedding a WOC
Dendrimers based on photoactive metal complexes. Recent advances
No full textRecent advances in the field of photoactive dendrimers containing metal complexes are reviewed. Dendrimers with [Ru(bpy)3]2+ as a core exhibit the characteristic [Ru(bpy)3]2+ type luminescence that can be (i) protected from external quenchers by the dendrimer branches and (ii) sensitized by chromophoric groups contained in the periphery of the dendrimer (antenna effect). Several examples of dendrimers fully based on transition metal complexes (i.e., containing a metal at each branching point of the dendrimer structure) have been investigated with the purpose of light harvesting. Dendrimers containing one or more free base and metal porphyrin units have been investigated for light harvesting and for a variety of other purposes. Scattered examples of other types of photoactive dendrimers are also reviewed. © 2001 Elsevier Science B.V. All rights reserved
Molecular Modelling and Simulations of Light-Harvesting Decanuclear Ru-Based Dendrimers for Artificial Photosynthesis
Full text linkThe structure of a decanuclear photo- and redox-active dendrimer based on Ru(II) polypyridine subunits, suitable as a light-harvesting multicomponent species for artificial photosynthesis, has been investigated by means of computer modelling. The compound has the general formula [Ru{(μ-dpp)Ru[(μ-dpp)Ru(bpy)2]2}3](PF6)20 (Ru10; bpy=2,2′-bipyridine; dpp=2,3-bis(2′-pyridyl)pyrazine). The stability of possible isomers of each monomer was investigated by performing classical molecular dynamics (MD) and quantum mechanics (QM) simulations on each monomer and comparing the results. The number of stable isomers is reduced to 36 with a prevalence of MER isomerism in the central core, as previously observed by NMR experiments. The simulations on decanuclear dendrimers suggest that the stability of the dendrimer is not linked to the stability of the individual monomers composing the dendrimer but rather governed by the steric constrains originated by the multimetallic assembly. Finally, the self-aggregation of Ru10 and the distribution of the counterions around the complexes is investigated using Molecular Dynamics both in implicit and explicit acetonitrile solution. In representative examples, with nine and four dendrimers, the calculated pair distribution function for the ruthenium centers suggests a self-aggregation mechanism in which the dendrimers are approaching in small blocks and then aggregate all together. Scanning transmission electron microscopy complements the investigation, supporting the formation of different aggregates at various concentrations
Ru(Ii)-dppz derivatives and their interactions with dna: Thirty years and counting
No full textTransition metal complexes with dppz-type ligands (dppz = dipyrido[3,2-a:2′,3′-c]phenazine) are extensively studied and attract a considerable amount of attention, becoming, from the very beginning and increasingly over time, a powerful tool for investigating the structure of the DNA helix. In particular, [Ru(bpy)2(dppz)]2+ and [Ru(phen)2(dppz)]2+ and their derivatives were extensively investigated as DNA light-switches. The purpose of this mini-review, which is not and could not be exhaustive, was to first introduce DNA and its importance at a biological level and research in the field of small molecules that are capable of interacting with it, in all its forms. A brief overview is given of the results obtained on the Ru-dppz complexes that bind to DNA. The mechanism of the light-switch active in this type of species is also briefly introduced along with its effects on structural modifications on both the dppz ligand and the ancillary ligands. Finally, a brief mention is made of biological applications and the developments obtained due to new spectroscopic techniques, both for understanding the mechanism of action and for cellular imaging applications
Photo-induced water oxidation: New photocatalytic processes and materials
No full textNew progress towards artificial photosynthetic methods and solar fuels will depend on the discovery of highly robust multi-electron catalysts and materials enabling light-activated water splitting with high quantum efficiency and low overpotential, thus mimicking the natural process
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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