Redox ligand complexes

The most important types of reactions are precipitation reactions, acid-base reactions, metal-ligand complexation reactions, and redox reactions. In a precipitation reaction two or more soluble species combine to produce an insoluble product called a precipitate. The equilibrium properties of a precipitation reaction are described by a solubility product. 

Figure 3. Schematic illustration of core/shell nanoparticle formation via redox transmetalation process. Metal ions (Mu) of reactant metal complexes (Mn-L ) are reduced on the surface of Mi nanoparticles while neutral Mi atoms are oxidized to Mi " by forming a Mi-ligand complex (Mi-Lj) as a resultant reaction byproduct. Repeating this process results in the complete coverage of shell layers on core metals. (Reprinted from Ref [145], 2005, with permission from American Chemical Society.)...

The concept of ligand complex was nicely demonstrated in the structures of complexes (495) (Cu-Cu 3.1172A 2/=-164cm-1)408 and (496) (Cu-Cu 3.097 A, 4.984A, and 5.108A).409 For both the complexes, spectroscopic and redox properties were also studied. 

The redox chemistry of macrocyclic ligand complexes has received much attention. There are several reasons for this. 

As mentioned previously, a large number of redox reactions involving macrocyclic ligand complexes have resulted in discrete changes in the unsaturation pattern of a variety of macrocyclic systems. Chemical, electrochemical, and catalytic reactions have been widely used to change the level of unsaturation in such systems. Although the mechanisms of the majority of such transformations are not well understood, it is clear that the reactions tend to proceed via prior change in the oxidation state of the central metal ion. 

Atom transfer radical polymerization (ATRP) [52-55]. Active species are produced by a reversible redox reaction, catalyzed by a transition metal/ligand complex (Mtn-Y/Lx). This catalyst is oxidized via the halogen atom transfer from the dormant species (Pn-X) to form an active species (Pn ) and the complex at a higher oxidation state (X-Mtn+1-Y/Lx). 

In general, the introduction of spatially hindered phenols into coordination compounds may produce stable free-radical forms [138b—140]. A series of metal complexes with redox ligands, containing derivatives of 2,6-di-t-butylphenols n- or a-connected, or vicinal fragments in the coordination environment of the central metal atom, were synthesized in this way 7i-aryl [141], Tt-cr-allyl [142] compounds, nitrile complexes [143], metal glioximates [144], salicylaldiminates [145,146], por-phyrines [147-149], and phthalocyanines [150,151],... 

Reinhoudt and co-workers (101-105) have reported a series of Schiff base macrocyclic polyether ligand complexes prepared via barium cation-templated Schiff base condensation of the appropriate polyether dialdehyde with a diamine, in the presence of a transition metal or uranyl acetate, followed by removal of the Ba2+ template cation on subsequent addition of guanidinium sulfate (Scheme 19). The copperdl) and nickeldl) complexes (62) and (63) exhibit reversible redox couples... 

Other donors that can form mixed-ligand complexes with dithiolene ligands include phosphorous-, nitrogen-, oxygen-, and other sulfur-based ligands. The resultant complexes are abundant and most of them are redox active. However,... 

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