Optical activity in coordination chemistry

In describing a stereoisomer, it is perhaps most important initially to define whether or not it is chiral. The origins of chirality (optical activity) in coordination compounds and important experimental results have been recently reviewed.112,113,121,122 The classical example of chirality or enantiomerism in coordination chemistry is that of octahedral complexes of the type [M-(bidentate)3]. These exist in the propeller-like,123 non-superimposable, mirror-image forms (13a) and (13b). Synthesis of this type of complex from M and the bidentate ligand in an achiral environment such as water results in an equimolar mixture of the two stereoisomers. The product... 

Oxalate (ox, 204 ) complexes of Cr° have been known since the very beginning of coordination chemistry. Thus, the resolution of chiral [Cr(ox)3] with strychninium counterion by Werner in 1912 prodnced the first optically active anionic coordination compound. There also exists a series of bis(oxalato) complexes of the type [Cr(ox)2X2] + , where X can be any of a variety of nentral donors (e g. H2O, NH3, etc.) or anionic ligands (e g. SCN, N3, etc.). These compounds have been used to study the mechanism of cis/trans isomerization and racemization of optically active octahedral coordination compounds. 

The coordination theory was promoted by the Swiss chemist Alfred Werner (1866-1919) in 1891. He became a professor in Zurich in 1893, and in 1913, he received the Nobel Prize in Chemistry for his investigations of complex compounds. Werner found many non-organic compounds with asymmetrical molecules that were also optically active in solutions. Such complex compounds include Co, Cr, and Fe. 

The resolution of optically active coordination compounds, a feat which shook chemistry to its innermost foundations ,72 gained for the coordination theory the widespread recognition for which Werner had been striving for so long. Nor was the theory s founder neglected, for two years later, largely in recognition of the most brilliant confirmation of [his] stereochemical views ,73 Werner was awarded the Nobel Prize in chemistry for 1913.74... 

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. 

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