Cobalt complexes supramolecular

Ethylenediaminetetraacetic acid, analogs, complexes of, 3 277 chelation by, 3 276-277 cobalt complex of, 3 281 complexes, 3 277-278 formation constant of, 3 273-274 -nickel, 3 17-18 stability of, 3 266-267 reaction with metal ions, 3 62 Ethylene dibromide, irradiation of, 5 196 4,5-Ethylenedithio-1,3-dithiole-2-thione based supramolecular complexes, 46 200-204 Ethylene glycol, 32 4... 

A chromophore such as the quinone, ruthenium complex, C(,o. or viologen is covalently introduced at the terminal of the heme-propionate side chain(s) (94-97). For example, Hamachi et al. (98) appended Ru2+(bpy)3 (bpy = 2,2 -bipyridine) at one of the terminals of the heme-propionate (Fig. 26) and monitored the photoinduced electron transfer from the photoexcited ruthenium complex to the heme-iron in the protein. The reduction of the heme-iron was monitored by the formation of oxyferrous species under aerobic conditions, while the Ru(III) complex was reductively quenched by EDTA as a sacrificial reagent. In addition, when [Co(NH3)5Cl]2+ was added to the system instead of EDTA, the photoexcited ruthenium complex was oxidatively quenched by the cobalt complex, and then one electron is abstracted from the heme-iron(III) to reduce the ruthenium complex (99). As a result, the oxoferryl species was detected due to the deprotonation of the hydroxyiron(III)-porphyrin cation radical species. An extension of this work was the assembly of the Ru2+(bpy)3 complex with a catenane moiety including the cyclic bis(viologen)(100). In the supramolecular system, vectorial electron transfer was achieved with a long-lived charge separation species (f > 2 ms). 

Some related examples with BR2 monocapped ligands are also known [181] and one of these molecules, 129, assembles to an interesting supramolecular structure, in which the cobalt(III) ions in a methylcobaloxime unit are coordinated to the pyridine residues of the bridging B(py)(OMe) group (Fig. 34). The dinuclear complex forms a large rectangular cage that is limited by the two pyridine residues and the cobaloxime moieties. The two pyridine... 

Chiper M, Meier MAR, Kranenburg JM, Schubert US. New insights into nickel(II), iron(II), and cobalt(II) bis-complex-based metaUo-supramolecular polymers. Macromol Chem Phys 2007 208 679-689. 

The complexation of coordination compounds may make it possible to control their photochemical behaviour via the structure of the supramolecular species formed. For instance, the binding of cobalt(m) hexacyanide by macrocyclic polyammonium receptors markedly affects their photoaquation quantum yield in a structure-dependent manner [8.73-8.77]. It thus appears possible to orient the photosubstitution reactions of transition-metal complexes by using appropriate receptor molecules. Such effects may be general, applying to complex cations as well as to complex anions [2.114]. 

A poly(propylenamine) dendrimer (11, Fig. 6.37) functionalised with poly-(N-isopropylacrylamide) (PIPAAm) (see Section 4.1.2) was used as dendritic host for anionic cobalt(II)-phthalocyanine complexes (a, b) as guests, which are held together by supramolecular (electrostatic and hydrophobic) interactions [57]. These dendritic complexes were investigated as catalysts in the above-mentioned oxidation of thiols, where they show a remarkable temperature dependence the reaction rate suddenly increases above 34°C. One attempted explanation assumes that the dendritic arms undergo phase separation and contraction above the Lower Critical Solubility Temperature (LCST). At this temperature the phthalocyanine complex site is more readily accessible for substrates and the reaction rate is therefore higher. 

The first example of chiral tetranuclear supramolecular assembly 5.27 was reported by Saalfrank and coworkers in 1988. Thus the complex [(NH3)4n(Mg (22)5] (5.27) was obtained by serendipity upon treatment of the doubly bidentate ligand 22, which is formed in situ from malonic ester and oxalyl chloride, with MeMgl in aqueous ammonium chloride solution (Scheme 5.13). Later an improved one-pot reaction was used to prepare such tetrahedral complexes of magnesium, manganese, cobalt and nickel by treating the bis(chelate) ligand 22, obtained in situ, with MeLi/MCl2 followed... 

The cobalt(II) complex is labile, and self-assembles to triple-helical [Co2(5-bismbmp)3] [24] which is readily oxidized to the cobalt(III) complex [Co2(5-bismbmp)3] which is sufficiently inert for the two enantiomers to be separated by classical methods [25]. The transformation of labile species to kinetically stable ones offers the possibility of using these elements as building blocks for further supramolecular construction. On the basis of our results with sophisticated ligand systems such as L232, we suspect that complicated, multicomponent self-assembly reactions without some element of kinetic stability will be rather difficult to develop. 

Fig. 7.15 Proposed structure of the supramolecular structure formed by complexation of meso-tetraMs((4-pyridyl)porphyrinato)cobalt (CoPCpy) ) with [Ru(NH3)3(H20)3] on a graphite electrode...

In the former case, polymers were assembled by complexation of a pyridyl-substituted porphyrin with the hexacoordinate metal ion, cobalt(II). The resulting supramolecular polymers, (60) (Figure 37), were characterized by UV/vis spectroscopy, NMR diffusion studies, and SEC. Polymers with concentration-dependent molecular weights up to 136 kDa (DP 100) formed, as indicated by SEC data. The dynamic nature of polymer formation was implied in the concentration dependence of the molecular weights as well as in capping studies with a porphyrin chain stopper [122],... 

Ozoemena [125] performed the anodic oxidation and amperometric sensing of hydrazine using a glassy carbon electrode modified with a cobalt(ll) phthalocya-nine-cobalt(n) tetraphenylporphyrin (CoPc-(CoTPP)4) supramolecular complex. This amperometric sensor displayed excellent characteristics for the determination of hydrazine in 0.2 M NaOH at low overpotential (+100 mV vs. Ag/AgCl), with very fast amperometric response time (1 s), linear range of 10-230 pmol LT, limit of detection of 1 pmol L and sensitivity of 0.0157 pA L pmol . ... 

Ozoemena KI (2006) Anodic oxidation and amperometric sensing of hydrazine at a glassy carbon electrode modified with cobalt (II) phthalocyanine-cobalt (II) tetraphenylporphyrin (CoPc-(CoTPP)4) supramolecular complex. Sensors 6 874—891... 

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