Polyfunctional ligands

Complexes of the type [AuRL] may contain a great variety of organic ligands such as alkyl, aryl, vinyl, or alkynyl, whereas the neutral donor ligand L is most commonly a tertiary phosphine. Also many polynuclear complexes are known which have the C-Au-L moiety with bridging polyfunctional ligands. Alkyl- or aryl-gold(I) complexes are usually synthesized... 

In the design of a homogeneous catalyst for the plain hydrogenation of thiophenes it is necessary to take into account that, unlike simple alkenes, (102) and (103) are polyfunctional ligands which can bind metal centers in a variety of bonding modes, often in a rapid equilibrium with each other.166-172,192 Among the possible coordination modes, the /-(S) and the 772-(C,C)... 

The ability of aluminium to adopt a wide variety of coordination numbers has led to the isolation of a large number of monomeric Al(III) hydroxide and organooxide complexes, many of which incorporate polyfunctional ligands, with the Group 13 metal centre in the coordination states 3-6. 

The same products can be obtained from NH4Tc04 as a precursor and cysteine. Earlier attempts to obtain technetium complexes with cysteine always resulted in the formation of a product contaminated with polymeric species [518]. Other attempts at chelating technetium with polyfunctional ligands that were accompanied by forma-... 

These few examples already demonstrate that polyfunctional ligands with C, symmetry permit unusual complex geometries with metals in a multitude of oxidation states. As a rule, extremely stable complexes are obtained, especially of early transition metals and metals in low oxidation states. 

The crystal stroctiires of a wide range of carboxylates have been described, the main features being that octahedral and tetrahedral coordination, sometimes distorted, are commonly observed and polymeric structmes, especially with polyfunctional ligands, are frequently found. 

The ligands discussed above are widely diversified certain of them can only serve as monodentate (imidazole, acetonitrile and isothiocyanate), bidentate (bipyridine, phenanthroline) or terdentate (terpyridine, TPTZ), others being the polyfunctional ligands with different donor sites may coordiate to the metal in various modes. In the latter case, the formation of chelate metallo-rings and/or the linking of the adjacent An coordination polyhedra is observed. 

This transformation is one of the most convenient syntheses of chelating polyfunctional ligands, studied extensively in organometallic chemistry. In this reaction, the practically non-coordinating nature of proton sponges (cf. equation 13) is effectively used. In the case of other bases, the process does not proceed (EtsN) or results in the formation of complex mixtures (f-BuOK). 

The multistep syntheses of the novel polyfunctional ligands H2C(3-Ph2Ppz)2 and (Me3SiCH(3-Ph2Ppz)2) have been reported by Otero (Scheme 13).217 The coordinating ability of these ligands towards a variety of early and late metal ions was studied. 

The simplification phase, previously exemplified by some authors [6], consists in the rather obvious operation of removing all the unnecessary elements that have no topological relevance, thus leaving only the essentials, represented by nodes and links (vertices and edges, respectively, in graph theory [7]). For instance, polyatomic nodes (like metal clusters or polyfunctional ligands) can be replaced by their barycenters. 

A complex with a ring structure results when a metal ion conbines with a polyfunctional ligand which is capable of occupying two or more positions in the coordination sphere of the metal ion. Such complexes containing ring structures are called chelates. An example of a chelate is shown by the structure ... 

Our structural investigations of hydrolytically polymerized Fe(III) have not been limited to the high molecular weight systems such as the Saltman-Spiro ball. Much more of our research, in fact, has been concentrated in the area of relatively simple binuclear Fe(III) complexes. The polyfunctional ligands EDTA (ethylenediaminetetracetate) and... 

In addition to multivalent interactions, the term polyvalency is used, especially if polyfunctional ligands bind to receptors on interfaces like cell membranes, which offer a large number (n 10) of two-dimensionally distributed binding sites, such as extended biological surfaces (e.g., bacteria, cells, viruses) [7,8]. 

This type of self-assembly can probably be expected for many other organo-indium derivatives of polyfunctional ligands. 

The interpretation of the solvent induced changes in the coordination equilibria was made difficult by the overlap of the multistep protonation (or complexation) equilibria of the polyfunctional ligands. The formation of protonation (or complexation) isomers, i.e. species with equal proton (or metal) - ligand ratios but of different structure] made the assignment of the conventionally... 

Type III The metal is part of a polymer chain or network. This type considers homochain or heterochain polymers with covalent bonds to the metal, coordinative bonds between metal ions and a polyfunctional ligand (coordination polymers), Ti-complexes in the main chain with a metal, cofacially stacked polymer metal complexes and different types (polycatenanes, polyrotaxanes, dendrimers with metals) (Figure 3). 

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