Metal ligand complex, acting

A second type of coordination mode for salen complexes is known also Peripheral functionalization of the salen ligand can provide sites for coordination to a secondary metal center (130, 132, 133) and the metal-salen complex acts as a true metalloligand. The central metal of the complex, not used in building the superstrucmre, can then be both coordinatively unsamrated and accessible to guest moieties. This combination of properties may lead to useful functions (e.g., catalysis). Several MOFs were described that have salen complexes as metalloligand linkers. 

An innovative procedure for the reproducible detection of metal ions using complexation schemes at PMEs was devised by Abruna and coworkers. " The systems developed rely on the presence of a redox couple in the polymer film in addition to immobilized complexing ligand sites. The redox couple, selected to have a formal potential removed from the metal-ligand complex to be detected, acts as an internal standard to allow facile evaluation of saturation effects, normally problematic in complexation studies with PMEs. The redox couple also increases the between- and within-film reproducibility by using ratiometric methods to... 

Almost all the kinetic studies on metaUomiceUar-mediated reactions have been carried out in the presence of either nonfunctional metallomicelles in which micellar head groups are incapable of acting as ligands for metal-ligand complex formation or induced functional metaUomiceUes in which micellar head groups act as effective ligands for metal-Ugand complex formation. 

As was suggested in the preceding discussion, most of the arene complexes isolated by metal-atom techniques are benzene derivatives. However, heterocyclic ligands are also known to act as 5- or 6-electron donors in transition-metal 7r-complexes (79), and it has proved possible to isolate heterocyclic complexes via the metal-atom route. Bis(2,6-di-methylpyridine)Cr(O) was prepared by cocondensation of Cr atoms with the ligand at 77 K (79). The red-brown product was isolated in only 2% yield the stoichiometry was confirmed by mass spectrometry, and the structure determined by X-ray crystal-structure analysis, which supported a sandwich formulation. 

Removing electrons from a metal atom always generates vacant valence orbitals. As described in Chapter 20, many transition metal cations form complexes with ligands in aqueous solution, hi these complexes, the ligands act as Lewis bases, donating pairs of electrons to form metal-ligand bonds. The metal cation accepts these electrons, so it acts as a Lewis acid. Metal cations from the p block also act as Lewis acids. For example, Pb ((2 g) forms a Lewis acid-base adduct with four CN anions, each of which donates a pair of electrons Pb ((2 ( ) + 4 CN ((2 q) -> [Pb (CN)4] (a g)... 

The following example demonstrates the implementation of known spectra and non-absorbing species into the algorithms. It is an aqueous spectrophotometric titration, investigating the complexation of a metal M by a ligand L to form the complex ML. The ligand also acts as a diprotic base and, additionally, the autoprotolysis of the solvent water needs to be taken into account. The complete model is ... 

There is some uncertainty whether this complex should be described as [Vm(bipy- )3] or as [V°(bipy)3], In fact, given that 2,2 -bipyridine can act either as a cr-donor or a n-acceptor, the metal-ligand bond in these complexes is constituted by a cr-bond between the lone pair of electrons of the nitrogen atom and an unoccupied s-orbital of the metal. Such electron donation, increasing the electron density on the metal, can in turn favour a back-bonding from the d-orbitals of the metal and the unoccupied rt -orbitals of the aromatic pyridine ring. In short, if the metal ion is in a high oxidation state pyridine will act as a a donor, whereas if the metal is in a low oxidation state pyridine will act as a n acceptor. 

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