Isomers of Metal Complexes

Submitted by JOHN L. BUBMEISTER and FRED BASOLOf Cheeked by S. E. JACOBSON and A. WOJCICKI  

Linkage isomerism in metal complexes was discovered in 1894 by Jorgensen.1 He prepared and characterized the nitrito 

It is noteworthy that the successful synthesis of nitrito-nitro linkage isomers for other metal ammines was designed only after the mechanism of formation of [Co(NH3)50NO]2+ and its rearrangement had been elucidated.4 It was found that the nitrito complex is readily formed without the cleavage of the Co—0 bond  

The kinetic product then slowly rearranges by an intramolecular process to the stable isomer [(NH3)5Co—N02]2+. On this basis it was reasoned that it should be possible to obtain other nitrito complexes by operating at an appropriate pH and under mild conditions. 

By taking advantage of the observation that the other ligands in a metal complex may alter the type of metal-atom bonding to an ambidentate ligand, it was possible to prepare thiocyanato (M—SCN) and isothiocyanato (M—NCS) linkage isomers. The syntheses of two such palladium (II) complexes are described below. 

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For a period of about 68 years after the original work of J0rgensen, no new types of linkage isomers of metal complexes were prepared. However, in recent years many such compounds have been obtained or their presence has been detected.7 The known examples are given in Table I. An examination of the... 

TABLE I Known Linkage Isomers of Metal Complexes... 

Cis-Trans Isomers of Metal Complexes as Potential Therapeutics... 

We have already used the HSAB principle as it applies to linkage isomers in metal complexes. This application to bonding site preference can also be used to show the behavior of other systems. For example, the reactions of organic compounds also obey the principles when reacting with nucleophiles such as SCN- or N02 ... 

The coupling of Naphtol AS or its phenyl-substituted derivatives with diazonium salts from variously substituted anilines in aqueous alkaline solution (section 4-11) gave incomplete reactions and impure products in some instances, probably because these coupling components have inadequate solubility in aqueous media. Pure dyes in ca. 90% yields were obtained by reaction in dimethylformamide in the presence of sodium acetate. Metallisation of these o,o -dihydroxyazo ligands with sodium chromium salicylate or a cobalt(II) salt gave metal-complex dyes in 80-100% yields [22]. Specific structural isomers of these complexes were identified by i.r., n.m.r., Raman and UV/visible spectroscopy [23]. 

The topologically defined region(s) on an enzyme responsible for the binding of substrate(s), coenzymes, metal ions, and protons that directly participate in the chemical transformation catalyzed by an enzyme, ribo-zyme, or catalytic antibody. Active sites need not be part of the same protein subunit, and covalently bound intermediates may interact with several regions on different subunits of a multisubunit enzyme complex. See Lambda (A) Isomers of Metal Ion-Nucleotide Complexes Lock and Key Model of Enzyme Action Low-Barrier Hydrogen Bonds Role in Catalysis Yaga-Ozav /a Plot Yonetani-Theorell Plot Induced-Fit Model Allosteric Interaction... 

Coordination isomers of metal ion-nucleotide complexes. For most metal ions, for example Mg, the metal... 

LAMBDA (or A-) ISOMERS OF METAL ION-NUCLEOTIDE COMPLEXES LANGMUIR ISOTHERM BIOMINERALIZATION MICELLE... 

NMR studies on Cp2Fe2(CO)2(CNMe)2 (186). As a consequence of these rules the six possible isomers of this complex (excluding optical isomers) (Fig. 3) should interconvert in two definite sets (26, 28, and 30 27, 29, and 31) in which it is not possible to convert members of the one set into members of the other set (assuming that there is no intermediate nonbridged structure with both isonitriles on the same metal atom). The NMR observations were in keeping with these predictions. 

Ray, R.K. and Kauffman, G.B. (1989) Chromatographic study of metal complexes, Part IV Thin layer chromatographic separation of cis from trails isomers of cobalt (III) mixed ligand complexes. Inorg. Chim. Acta, 162, 45-48. 

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