Coordination chemistry optical isomers

The crystal structures of numerous other complexes of various coordination numbers have been determined, completely and directly confirming Werner s earlier indirect configurational proofs by the preparation of isomers and resolution of optically active compounds (see Section 4). Today, the terminology and concepts of coordination chemistry are universally used in crystallography. 

Rhodotorulic acid (RA), a dihydroxamate siderophore, forms dimeric complexes with iron, aluminium and chromium of the stoichiometry M2(RA)3 at neutral pH 36 188). The coordination chemistry of this siderophore is probably the most complicated of the siderophores. The combination of cis-trans, A and A configurations of two iron miters, connected by three RA molecules, makes 42 non-redundant isomers theoretically possible each can be simulated by molecular models. Recently three different isomers or mixtures of isomers of Cr2RA3 were separated by reversed phase HPLC-chromatography177). The visible spectrum of the most abundant fraction corresponds to the cis isomer the two other fractions are very similar to the visible spectrum of the trans Cr(men)3 isomer. The CD spectra, in comparison with the Cr(men)3 model complex, show two different optical isomers, assigned as A -trans and A -trans. The A isomer preparation seems also to contain a certain amount of the A configuration. This is the first time that two different, kinetically stable optical isomers have been isolated from the metal complexes of a siderophore 177). 

Despite the increase in our understanding of microbial iron transport from these studies, much remains unknown. For example, one of our original queries remains unanswered. Is recognition of the iron(III) siderophore complex and subsequent active transport into the cell dependent on one optical isomer This and other questions concerning the coordination chemistry of sidero-phores remain to be answered. 

Define the terms diamaffwtic 2mAparamagnetic. What feature of electronic structure is directly related to these properties What are three common metal coordination numbers found in coordination chemistry Give the shape usually associated with each of the common coordination numbers. Several isomers are possible for [Co(en)(NH3)(H20)2Cl]. (Two of the isomers have optical isomers.) How many isomers can you draw Draw the strucmre of an isomer that does not have an optical isomer. Draw the structure of an isomer that would have an optical isomer. Hint en is not large enough to bind at mms locations.)... 

Additional opportunities for optical activity arise in molecules containing chelating ligands (A-A). For example, a compound of general formula M(A-A)2B2 has two geometric isomers, one of which is chiral. The propeller-like tris-chelated M(A-A)3 compounds are always chiral. Werner and his collaborators took advantage of the ready optical activity of such complexes to provide additional proof that the coordination spheres of his many and varied cobalt compounds were octahedral. After 20 years of work, Werner s coordination theory was thoroughly established, and he received the Nobel Prize in chemistry in 1913. In a final positive proof, Werner and co-workers... 

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