Type II ligands

Work in our group has been concerned with C2u-symmetrical ligands in which a central heterocycle carries four aliphatic side-arms (type I ligands) (5). In other cases, the donor set AE4 (A apical donor, E equatorial donor) has the same overall symmetry, but consists entirely of heteroaromatics (type II ligands). Thirdly, two ligands have so far been described which have overall Cs symmetry, in which the central , apical donor atom is part of an aliphatic backbone (type III ligands). 

The first report of a type II ligand dates back to 1981 (1,2). In view of the biochemical relevance of imidazol ligands, Tagaki and co-workers synthesized a pyridine carrying four imidazolyl substituents (5) and... 

ISO ms and finally slower disappearance with formation of the fully reduced enzyme. But the regrowth of the type II spectrum is of a rate comparable to the reduction of the type III Cu(II) site and consistent with the participation of the type II ligand binding site in the reduction of the type III pair. 

Figure 1-5. Type II Ligand of a metal complex as part of a macromolecule.

Figure 2 Type II Ligand of metal complexes, chelates as part of linear or crosslinked macromolecules.

When naming complex ions the number and type of ligands is written first, followed by the name of the central metal ion. If the complex as a whole has a positive charge, i.e. a cation, the name of the central metal is written unchanged and followed by the oxidation state of the metal in brackets, for example [Cu(N 113)4] becomes tetra-ammine copper(II). A similar procedure is followed for anions but the suffix -ate is added to the central metal ion some examples are ... 

The Fas ligand or FasL is a type II transmembrane protein that belongs to the tumor necrosis factor (TNF) family. The binding of Fas ligand with its receptor induces apoptosis. 

Although MR also binds glucocorticoids, its main ligand in classical mineralocorticoid target tissues such as kidney and colon is aldosterone ( d 1.3 nM). This can be granted to the ability of 11 (3-hydioxysteroid dehydrogenase type II (11 (3-HSD II) to convert active cortisol into its inactive metabolite cortisone in these tissues. Since aldosterone is no substrate for this enzyme it can readily bind to MR, leading to exclusive occupation of the receptor by aldosterone. In contrast, no such mechanism exists in brain and presumably... 

The names of coordination compounds can become awesomely long because the identity and number of each type of ligand must be included. In most cases, chemists avoid the problem by using the chemical formula rather than the name itself. For instance, it is much easier to refer to [FeCl(H20)5]+ than to pen-taaquachloroiron(II) ion, its formal name. However, names are sometimes needed, and they can be constructed and interpreted, in simple cases at least, by using the rules set out in Toolbox 16.1. Table 16.4 gives the names of common ligands and their abbreviations, which are used in the formulas of complexes. 

The outer ligands in M3Q4L9 (type-I) and M3Q7L6 (type-II) clusters can be easily replaced through nucleophilic substitution reactions. These reactions are discussed separately for each cluster type. 

For L=NH3 (1) and L=Pr2NH (3), the isotherms are of type II as expected for non-porous materials [27]. Sample 2 shows a significant uptake at 0.6

narrow particle-size distribution which results in a more regular packing with interparticle pores of size similar to that of the particles [27]. The latter shows that the ligand-assisted synthesis does not only allow one to affect the total surface area and particle size, but also the size distribution which is an important tool for tailoring the particle properties. 

In 2008, Que and coworkers reported an asymmetric version of the dihydroxylation with a new type of ligands bearing bipyrrolidine as the chiral backbone [71]. The corresponding iron(II) complex showed general activity in the dihydroxylation of various olefins using H202- Satisfactory results are obtained with aliphatic as well as with aromatic olefins. For example, dihydroxylation of styrene gave styrene oxide and 1-phenylethane-1,2-diol in <1% and 65% yield, respectively (Scheme 10). 

The wavenumbers of the MMCT transition between Pt(II) and Pt(IV) are related to the Pt(II)-Pt(IV) distance in the chain, as follows from a study of these compounds using different types of ligands. This relation is hnear [97]. ff the linear curve is extrapolated to a MMCT transition energy of zero, we obtain a distance equal to twice the Pt(IV)-ligand distance. This is the situation in which the Ugand, for example Cl or Br , is placed in between the two platinum ions, i.e. in which the difference between the platinum ions vanishes. 

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