Metal complexation terpyridines

Construction of one-dimensional multicomponent molecular arrays, transition metal complexes with terpyridines and/or porphyrins as ligands 98EJI1. 

Bipyridines were efficiently used in supramolecular chemistry [104], Since the molecule is symmetric no directed coupling procedure is possible. In addition, 2,2 6/,2//-terpyridine ligands can lead to several metal complexes, usually bis-complexes having octahedral coordination geometries [105,106], Lifetimes of the metal-polymeric ligand depend to a great extent on the metal ion used. Highly labile complexes as well as inert metal complexes have been reported. The latter case is very important since the complexes can be treated as conventional polymers, while the supramolecular interaction remains present as a dormant switch. 

Redox molecules are particularly interesting for an electrochemical approach, because they offer addressable (functional) energy states in an electrochemically accessible potential window, which can be tuned upon polarization between oxidized and reduced states. The difference in the junction conductance of the oxidized and the reduced forms of redox molecules may span several orders of magnitude. Examples of functional molecules used in these studies include porphyrins [31,153], viologens [33, 34,110,114,154,155], aniline and thiophene oligomers [113, 146, 156, 157], metal-organic terpyridine complexes [46, 158-163], carotenes [164], nitro derivatives of OPE (OPV) [165, 166], ferrocene [150, 167, 168], perylene tetracarboxylic bisimide [141, 169, 170], tetrathia-fulvalenes [155], fullerene derivatives [171], redox-active proteins [109, 172-174], and hydroxyquinones [175]. 

In most cases, metal ion coordination by a dendrimer takes place by units that are present along the dendrimer branches (e.g., amine, imine, or amide groups) or appended at the dendrimer periphery (e.g., terpyridine, cathecolamide ligands). When multiple identical coordinating units are present, dendrimers give rise to metal complexes of variable stoichiometry and unknown structures. Luminescent dendrimers with a well defined metal-coordinating site have been reported so far [16, 17], and the most used coordination site is 1,4,8,11-tetraazacyclotetradecane (cyclam). 

Schubert US, Eschbaumer C Angew Chem Int Ed (2002) 41 2892-2926 Macromolecules containing bipyridine and terpyridine metal complexes towards metallo-supramolecular polymers... 

Pyridine-based ligands which have been used for dendrimers are 2,2-bipyridine (bpy) 17,2,3-bis(2-pyridyl)pyrazine (2,3-dpp) 18 and its monomethylated salt 19, and 2,2 6, 2"-terpyridine 20. Their transition metal complexes possessing dendritic structures were first reported in the collaborative work of Denti, Campagne, and Balzani whose divergent synthetic strategy has led to systems containing 22 ruthenium centers. - The core unit is [Ru(2,3-dpp)3] 21 which contains three... 

Dale Margerum Ralph Wilkins has mentioned the interesting effect of terpyridine on the subsequent substitution reaction of the nickel complex. I would like to discuss this point—namely the effect of coordination of other ligands on the rate of substitution of the remaining coordinated water. However, before proceeding we should first focus attention on the main point of this paper-which is that a tremendous amount of kinetic data for the rate of formation of all kinds of metal complexes can be correlated with the rate of water substitution of the simple aquo metal ion. This also means that dissociation rate constants of metal complexes can be predicted from the stability constants of the complexes and the rate constant of water exchange. The data from the paper are so convincing that we can proceed to other points of discussion. 

By substituting either the metal (Os(II), Co(II)) or the ligand, (e.g., terpyridine tpy), a variety of metal complexes have been obtained and used as building blocks of dendrimers. As in the case of [Ru(bpy)3]2 +, the first oxidation process is metal centered and reductions are ligand centered. Metal complexes can be placed at the... 

In this section, we describe the fabrication of metal complex oligomer and polymer wires composed of bis(terpyridine)metal complexes using the bottom-up method.11 13 This method has an advantage in fabricating organized structures of rigid redox polymer wires with the desired numbers of redox metal complexes. We also present a new electron-transport mechanism applicable to the organized redox polymer wires-coated electrode. 

In this chapter, we presented three different systems of molecular assemblies using molecular wires. The first involved the fabrication of the molecular wire system with metal complex oligomer or polymer wires composed of bis(terpyridine)metal complexes using the bottom-up method. This system showed characteristic electron transfer distinct from conventional redox polymers. The second involved the fabrication of a photoelectric conversion system using ITO electrodes modified with porphyrin-terminated bis(terpyr-idine)metal complex wires by the stepwise coordination method, which demonstrated that the electronic nature of the molecular wire is critical to the photoelectron transfer from the porphyrin to ITO. This system proposed a new, facile fabrication method of molecular assemblies effective for photoelectron transfer. The third involved the fabrication of a bioconjugated photonic system composed of molecular wires and photosystem I. The feasibility of the biophotosensor and the biophotoelectrode has been demonstrated. This system proposed that the bioconjugation and the surface bottom-up fabrication of molecular wires are useful approaches in the development of biomo-lecular devices. These three systems of molecular assemblies will provide unprecedented functional molecular devices with desired structures and electron transfer control. 

Abstract The photochemical properties of transition metal complexes, such as those of iridium(III) or ruthenium(II), can be exploited in various ways to generate charge-separated (CS) states, in relation to the mimicry of the natural photosynthetic reaction centres, or to set multicomponent compounds or assemblies in motion. The first part of the present chapter summarizes the work carried out in our groups (Bologna and Strasbourg) in recent years with iridium(III)-terpy complexes (terpy 2,2,6,6"-terpyridine). The synthesis of multicomponent iridium(III) complexes in reasonable yields has been... 

As rationally designed multinuclear catalysts for transesterification of HPNPP, metal complexes such as 5 have been designed [42]. By random attachment of lauryl groups and Ni(n) complexes of terpyridine (TP) to PEI (6) we have synthesized a polymer that has much higher catalytic activity than 5 for the same reaction [43]. The contents of the pendant groups were varied in several combinations, and the best catalyst (]Ni(ii)TP]5Lau12PEI) contained 5 residue mol% Ni(n)TP and 12 residue mol% lauryl group. 

Many analytes that have basic sites prone to protonation, display pH-dependent electrochemistry. The redox properties of metal complexes of H2O, OH, and often display pH-dependent electrochemistry as demonstrated by Meyer et al. for the complex [M(tpy)(bpy)0] + (M = Ru or Os tpy = 2,2, 2"-terpyridine). These complexes have been studied probing their electrochemistry over a wide range of pH. CV and DPP were used to determine Ei/2 for the Ru and Ru redox couples of the complex [Ru(tpy)(bpy)0] + from pH 0 to 13 (Figure 4) and the Nemst equation (2) was used to fit the data. 

On the coordination chemistry side, ligand substitution on metal complexes in ILs has attracted quite some interest. This is mainly due to the fact that both spectroscopic and catalytic properties are strongly governed by the nature of the ligands and the stability of their bond to a metal center. Begel et al. have studied the role of different ILs on ligand substitution reactions on [Pt(terpy)Cl]+ (terpy = 2,2 6, 2"-terpyridine) with thiourea with stopped-flow techniques. The substitution kinetics show similar trends if compared to conventional solvents with similar polarities. Moreover, much like in conventional solvents, the authors find an associative character of the substitution reaction [205], These results are essentially supporting an earlier study by Weber et al., who found the same behavior [206],... 

Recent developments in the supramolecular chemistry of terpyridine-metal complexes 04CSR373. 

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