Macrocyclic ligands—continued

Fe complex of 2,2 -bipyridine-3,5 -dicarboxylic acid but the pyridine-4-carboxylic acid was observed not to be photosensitive in the presence of Fe ions. The photochemistry of low-spin Fe complexes with macrocyclic ligands continues to be a field that attracts interest. Irradiation of the charge-transfer bands of [Fe(TIM)(OMe)(MeOH)] + (TIM = 2,3,9,10-tetramethyl-l,4,8,ll-tetraazacyclotetradeca-l,3,8,10-tetraene) and of [Fe(DMG)2(OMe)(MeOH)] (DMG = dimethylglyoxime), was found to lead to oxidation of the co-ordinated MeOH and reduction of the metal centre. These photoreactions have been attributed to the population of methoxy-to-Fe CT states. 

Apart from this one-reaction type, the routine use of metal template procedures for obtaining a wide range of macrocyclic systems stems from 1960 when Curtis discovered a template reaction for obtaining an isomeric pair of Ni(n) macrocyclic complexes (Curtis, 1960). Details of this reaction are discussed later in this chapter. The template synthesis of these complexes marked the beginning of renewed interest in macrocyclic ligand chemistry which continues to the present day. 

However, it remains a fact that an enormous number of macrocyclic ligands have been, and new examples continue to be, made using template methods. 

The roles of the copper enzymes in electron transport, oxygen transport, and oxidation reactions have guaranteed continued interest in their study. In addition to studies of the natural compounds, there have been many attempts to design model structures of these enzymes, particularly of the binuclear species. Many of these include both nitrogen and oxygen donors built into macrocyclic ligands, although sulfur has been used as well. ... 

The field of nickel complexes with macrocyclic ligands is enormous and continuous interest in this area in recent years has resulted in innumerable publications. A number of books and review articles are also available covering the general argument of the bonding capability of the various macrocyclic ligands towards transition and non-transition metals Synthetic procedures for metal complexes with some tetraaza macrocycles have been reported.Kinetics and mechanism of substitution reactions of six-coordinate macrocyclic complexes have also been reviewed. 

Additional improvement relates to solution properties such as ion solvation and conductivity. A typical example is macrocyclic ligands such as crown ethers, whose preferential coordination of Li enhances the Li+ transference number and cycling efficiency of graphitic anodes. " - " However, the studies along these lines have not been continued probably due to the lack of anodic stability. 

Synthetic developments in the area of Supramolecular Chemistry are currently leading to a massive production of new macrocycles. The driving force for this continuous growth is the search for selective hosts to target a particular neutral or ionic species. There is no doubt that the impact produced by the discovery of macrocyclic ligands such as the crown ethers [1] and the cryptands [2] resulted from their cation complexation and this prompted us to consider the thermodynamic characterisation of these systems (mainly cryptands) which has been extensively reported [3-5]. Calixarenes, an important class of macrocyclic compounds, are products of the base-catalysed condensation reaction of p-substituted phenols and formaldehyde [6, 7]. These compounds are characterised by their low solubilities in most solvents, although until recently [8], no quantitative data has been reported. Functionalisation of the lower or upper rim of parent calix[n]arenes has... 

A large amount of work has been devoted to N-binding macrocyclic complexes of Ni, Cu and Fe, which yield imine ligand products. Bidentate amine ligands, mainly ethylenediamine (en), have been used with Ru and Os complexes. The oxidation of coordinated ethylenediamine and related ligands stops at the diimine stage and does not continue to the dinitrile. The a,a -diimine entity -N=C-C = N- formed in the four-electron oxidation is particularly stable (93). 

One of the earliest Schiff base macrocycles to exhibit a haemocyanine-like structure was the copper(II) perchlorate complex of 5.5 which binds readily to azide or hydroxide.8 The azide complex exhibits two square pyramidal copper binding domains with the basal plane occupied by one pyridyl nitrogen atom and two imine functionalities as well as a terminal azide ligand. The apices of the two pyramidal coordination polyhedra are linked by a single bridging azide anion. Continuing the biomimetic theme, manganese (II) cascade complexes of the unsymmetrical 5.6 have... 

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