Metal complexes formation

Certain dyes when appHed by the afterchrome method are oxidized prior to metal complex formation. Examples iaclude. Chromotrope EB [3567-69-9] (52) (Cl Acid Red 14 Cl 14720) (naphthionic acid — l-naphthol-4-sulfonic acid) ia which a hydroxyl group is iatroduced by oxidation at the... 

With azo dyes derived from 4,5-dihydroxy-2,7-naphthalenedisulfonic acid [148-25-4] (chromotropic acid) as the coupling component, metal complex formation occurs with the perihydroxy groups without oxidation. 

Molecules having only a sulfoxide function and no other acidic or basic site have been resolved through the intermediacy of metal complex formation. In 1934 Backer and Keuning resolved the cobalt complex of sulfoxide 5 using d-camphorsulfonic acid. More recently Cope and Caress applied the same technique to the resolution of ethyl p-tolyl sulfoxide (6). Sulfoxide 6 and optically active 1-phenylethylamine were used to form diastereomeric complexes i.e., (-1-)- and ( —)-trans-dichloro(ethyl p-tolyl sulfoxide) (1-phenylethylamine) platinum(II). Both enantiomers of 6 were obtained in optically pure form. Diastereomeric platinum complexes formed from racemic methyl phenyl (and three para-substituted phenyl) sulfoxides and d-N, N-dimethyl phenylglycine have been separated chromatographically on an analytical column L A nonaromatic example, cyclohexyl methyl sulfoxide, did not resolve. 

Seward, T.M. (1981) Metal complex formation in aqueous solutions at elevated temperatures and pressures. In Rickard, D.T. and Wickman, F.E. (eds.). Chemistry and Geochemistry of Solutions at High Temperatures and Pressures, Phys. Chem. Earth, 13 and 14, 113-132. 

The ability of transition metal ions, and especially chromium (as Cr3+), to form very stable metal complexes may be used to produce dyeings on protein fibres with superior fastness properties, especially towards washing and light. The chemistry of transition metal complex formation with azo dyes is discussed in some detail in Chapter 3. There are two application classes of dyes in which this feature is utilised, mordant dyes and premetallised dyes, which differ significantly in application technology but involve similar chemistry. 

In the sections which follow processes based on metal complex formation are described in the order they occur in the flowsheets in Figures 2 and 3, i.e.,... 

Some of the types of equilibria involved in the unit operations separation and concentration are listed in the introduction, Section 9.17.1. Those which depend most on coordination chemistry, and for which details of metal complex formation are best understood, are associated with hydrometallurgy. Once the metal values have been transferred to an aqueous solution, the separation from other metals and concentration can be achieved by one of the following processes.3... 

It will not be lost on the reader that, while PHOTOFRIN and compounds (3), (5) and (6) contain no metal, they would be expected to be excellent ligands. Are metal complexes useful as PDT photosensitizers Indeed, they are, and may be expected in the future to become more important. The rest of this chapter is about this aspect it will emphasize metal complex formation and properties in relation to PDT. The synthesis of ligands, while of crucial importance, will not usually be treated here in detail, but leading references to relevant synthetic organic chemistry will be provided. The synthesis of porphyrins and related compounds has been considered in several monographs and reviews (porphyrins,46 47 phthalocyanines48). 

Subtle differences in the behavior of azoarenes toward cobalt carbonyl derivatives are observed in regard to metal-complex formation. Azobenzene is transformed by dicobalt octacarbonyl in processes of orthometallation and carbonyl insertion into 2-phenylindazolin-3-one (see Section IV,D,2). In contrast, cyclopentadienylcobalt dicarbonyl effects N—N bond cleavage, and carbonylation of the isolable complex 88a provides 1 -phenylbenzimid-azolin-2-one (Scheme 106).171... 

It has been proposed that the first stage of alkali metal complex formation by dibenzo-30-crown-10 in methanol involves a fast ligand conformational change which is then followed by a stepwise substitution of the coordinated solvent by the ligand (Chock, 1972) ... 

Direct dyes have only modest fastness to washing, which may be improved by after-treatments such as metal-complex formation (section 5.5.3) or by diazotisation of the dye on the fibre and further coupling of the diazonium salt with an insoluble coupling component (section 1.6.14). In addition to their use on cotton and viscose, direct dyes are important in the dyeing of leather. The cheapest members of this class are also used in the coloration of paper, since for this purpose fastness properties are largely irrelevant and price is all-important. 

Metal-complex formation entails the interaction of one or more organic ligands with a multivalent metal cation. This brings about certain fundamental changes in the characteristics of the components of the complex. 

Metal complex formation considerably improves both lightfastness and weatherfastness in o,o -dihydroxyazo and o,o -dihydroxy azomethine pigments, usually compromised by distinctly dull color. 

Ultrasonic absorption played a major historical role in an understanding of the mechanisms of metal complex formation. It has also been used to study stereochemical change in metal... 

The rate of metal complex formation is often modified (usually enhanced) by the presence of a charged interface in the aqueous phase. This may be provided by ionic micelles, e. g., SDS, microemulsions or polyelectrolytes. jjjg reactions of Ni + and Co with hydrophobic ligands pan, pap and pad 14-16 are popular ones for examining effects, since they are well characterized in the bulk water. The simple model (4.126)... 

The ability of metal ions to accelerate the hydrolysis of a variety of linkages has been a subject of sustained interest. If the hydrolyzed substrate remains attached to the metal, the reaction becomes stoichiometric and is termed metal-ion promoted. If the hydrolyzed product does not bind to the metal ion, the latter is free to continue its action and play a catalytic role. The modus operandi of these effects is undoubtedly as a result of metal-complex formation, and this has been demonstrated for both labile and inert metal systems. Reactions of nucleophiles other than HjO and OH will also be considered. 

Seward T. M. (1981). Metal complex formation in aqueous solutions at elevated temperatures and pressures. Phys. Chem. Earth, 13 113-132. 

Anderegg G, Raber M (1990) Metal Complex Formation of a New Siderophore Desferrithi-ocin and of Three Related Ligands. J Chem Soc Chem Commun 1194... 

Guanidine forms salts with such relatively weak acids as nitromethane, phthalimide, phenol and carbonic acid [20], Interactions between carboxylate anions of proteins and added guanidinium ion are thought [19, 56] to be weaker than the interactions with ammonium ions the role of guanidinium-carboxylate interactions in stabilizing natural protein conformations has been discussed [36c]. A few reports of metal complex formation by guanidines [57-60], and aminoguanidines [61] have appeared. 

The effect of cation type on the magnitude of the log K value for metal-complex formation may be found by comparing cations of the same charge and similar ionic radii having noble gas electronic structures with those having pseudo-noble gas and pseudo-noble gas +ns2 electronic structures. Also, comparisons should be made in the region of optimum stability for the cations involved. The data in Table 3 show such com-... 

Several effects can influence the electronic structure of Cjq upon metal complex formation. One is the removal of one double bond from the remaining 29 fullerene double bonds. As in any polyene system, this decreased conjugation is expected to raise the energy of the LUMO and therefore decreases the electron affinity of the system. Conversely, the d-orbital backbonding transfers electron density from the metal into n orbitals of the remaining double bonds, which also decreases the electron affinity. 

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