Other Metallomacrocycles

Other supramolecular structures such as catenanes and rotaxanes can be formed using zinc as a template ion for example, a benzylic imine catenate formed by Leigh et a/.288 The reversible five-component assembly of a [2]catenane from a chiral metallomacrocycle and a dinaphtho-crown ether has been achieved. Zinc is used as the metal component and drives assembly via the coordination to a bipyridyl unit 7r interactions between the aromatic components are also... 

Fig. 2a-c. Some structural motifs for the parallel stacking of planar metallomacrocycles. Motif (a), which is the most important, is often called the metal-over-metal arrangement. Motif (b) is often called the slipped-stack arrangement. Many other motifs are possible, (c) being but one example... 

M—C a bonds are very few. In this chapter more precisely, larger metallomacrocycles with at least one M—C a bond with or without additional heteroatoms are reviewed. Unlike in other chapters, here the compounds are reviewed on the basis of the metal atom that is present in the ring, since the generalization of the synthesis, structure elucidation, and physical and chemical properties of all titled metallomacrocycles is rather intricate. Hence the chapter is framed to focus on two classes of metallomacrocycles (i) with mercury atoms, and (ii) with platinum and/or palladium atoms. 

The synthesis of the other mentioned metallomacrocycles, e.g. tetra(2,3-naphtho)porphyrinatometal complexes (2,3-TNPM) or octaethylporphyrins (OEPM), is not as straightforward. 

As, with the exception of the mentioned oxidized compounds, the metallomacrocycles do not crystallize forming columnar quasi-one-dimensional structures, one of the prerequisites for conductivity is not met. In addition the stacking repeat distances and the donor-acceptor distances in doped compounds cannot be controlled in any way. By using oxidizing dopants other than halogens, e.g. quinones, integrated stacks can be formed leading to insulators. 

In a recent study [111], it has been discussed that the changes in the formal potential of the catalyst could explain the high catalytic activity of ORR that has been obtained by heat treatment of metallomacrocyclics and other starting materials. For example, when comparing data obtained with heat-treated catalysts prepared by very different techniques and starting materials, not necessarily involving metalloma-crocyclic complexes [112], a correlation of log i (as currents normalized per mass of catalysts) vs. the formal potential of the catalyst gives what could be considered a linear correlation (see Fig. 7.21). 

Chapters 7-12 focus on the electrocatalysis of carbon-based non-precious metal catalysts. The unique properties and fuel cell applications of various carbon based catalysts are intensively discussed in these chapters. Chapter 7 summarizes the fundamental studies on the electrocatalytic properties of metallomacrocyclic and other non-macrocyclic complexes. Chapter 8 and 9 review the progress made in the past 5 years of pyrolyzed carbon-supported nitrogen-coordinated transition metal complexes. Chapter 10 gives a comprehensive discussion on the role of transitional metals in the ORR electrocatalysts in acidic medium. Chapter 11 introduces modeling tools such as density functional theory (DPT) and ah initio molecular dynamics (AIMD) simulation for chemical reaction studies. It also presents a theoretical point of view of the ORR mechanisms on Pt-based catalysts, non-Pt metal catalysts, and non-precious metal catalysts. Chapter 12 presents an overview on recent progresses in the development of carbon-based metal-free ORR electrocatalysts, as well as the correlation between catalyst structure and their activities. 

Other interesting systems that show catalytic activity is a variety of molecules that contain thiol groups [39 1]. Studies of the electrooxidation of thiols to give disulfides have shown that the catalytic activity of the molecular electrodes of gold. In this case, the metallomacrocycles of Co and Fe have exhibited the high activity. A very interesting case corresponds to the oxidation of L-cysteine and... 

N4 metallomacrocyclic compounds are highly versatile molecules that adsorb veiy strongly onto graphite and other electrodic surfaces in the form of monolayers. 

Dynamic equilibrium between the bis-ruthenium metallomacrocycle 325, ligand syn-tone 241, and a RueLg coordination capsule 629 (Scheme 4.96) is reported in [93] to be shifted in the direction of the corresponding host-guest 1 2 cage complex by addition of coronene as an appropriate guest In this coordination capsule, the triazine ligand syntones are stacked on top of each other, and two coronene molecules are sandwiched between them. 

Use of an uncoordinating solvent allowed obtaining 1 1 cage complex of C02L4 coordination capsule 780 (Scheme 4.194) with one encapsulated and two outside-coordinated tetra-fluoroborate anions [199] its caged BF4 anion forms a donor-acceptor Co-F bond of 2.31 A, and the Co... Co distance is approximately 6.9 A. The use of other cobalt(II) salts (in particular, its nitrate or chloride) gave either a ID coordination polymer or a metallomacrocyclic complex, respectively no template effect of these anions in... 

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