Isomer, optically active inorganic

The importance of the theory was further demonstrated by the discovery of the existence of optically active inorganic compounds, and the isolation of the exact number of optical isomers theoretically possible for the spatial arrangement of the atoms.1 Friend 2 and others criticised the theory on the grounds that in simple compounds, such as sodium chloride or cobaltous chloride, the chlorine is ionised and yet is attached to sodium or cobalt atom directly, whereas in the ammino-coinpounds the acid capable of ionisation is that which is not directly attached to metal. For instance, in chloro-pentammino-cobaltic chloride, [CoCI(NH3)5]C12, it is the chlorine outside the first zone which is ionised in solution. Also, the dissociable acidic groups are not attached to any point within the complex, but simply hover round the central complex in an indefinite manner. Thus a definite valency for ionisable... 

This purely inorganic compound was resolved into its isomers by Werner as final proof that optical activity was the property of the central coordinating atom only,... 

Molecules that show optical activity have no plane of symmetry. The commonest case of this is in organic compounds in which a carbon atom is linked to four different groups. An atom of this type is said to be a chiral centre. Asymmetric molecules showing optical activity can also occur in inorganic compounds. For example, an octahedral complex in which the central ion coordinates to six different ligands would be optically active. Many natur y occurring compounds show optical isomerism and usually only one isomer occurs naturally. 

The bulk of the work has been carried out using complexes of the type [M(bidentate)2X2] where bidentate is a bidentate ligand and X is monodentate. Anotha important area deals with the loss of optical activity of resolved octahedral complices. These reactions can be very fast or very slow and have long scinated inorganic chemists. In a number of cases the loss of optical activity (racemisation) is rdated to cis treats isomerisation. For example, in the [M(bidentate)2X2] complexes, the enantiomaic cis-isomer may lose its optical activity by isomeri g to the optical inactive ti-ans-isomer. Early and subsequent work on cis treats isomerisation and racemisation of octahedral metal complexes has been summarised and detailed in various books and reviews [ 1-6]. 

Inorganic and metal-organic compounds also have conformations and isomers, including optical isomers. It is expected that these various conformers and isomers will also have varying biological activities. 

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