Geometrical isomerism platinum complexes

Geometric isomerization of square-planar platinum(II) and palladium(II) complexes... 

Geometric isomerism is an important feature of the chemistry of square-planar compounds and has been studied in detail for palladium(II) and, especially, platinum(II) complexes. A pair of isomeric compounds will differ in thermodynamic stability and, under appropriate conditions. 

Pairs of geometric isomers differ from each other in their standard free energies of formation. However, the differences are typically not large. In the case of labile complexes, one isomer will be transformed into the thermodynamically favored form as equilibrium is reached. However, in the case of inert complexes, the conversion of one isomer into the other can be inhibited. In such cases, it may prove possible to study redox equilibria without the problem of an accompanying isomerization. Platinum and ruthenium chemistry has provided many examples of such systems. 

The cis-trans isomerization of square-planar transition metal complexes, in particular those of platinum(II) and palladium(II), can be understood by comparison of the trans-effects of the individual ligands (Chapter 1). This approach predicts the favored direction of isomerization for a large group of complexes with ligands of different types. In this Section examples of geometric isomerization which are not adequately explained by the trans-effect are considered and it is shown that solid state effects can influence the outcome of such reactions. 

The synthesis and antitumour properties of DACH platinum(II) complexes containing a variety of different types of leaving ligand have been reported [38, 39, 60-67]. Although early studies with the compounds were content to utilize mixtures of geometric and optical isomers, the realization that the stereochemistry of the DACH ligand influenced antitumour activity underscored the importance of working with isomerically pure forms of the diamine [68-70],... 

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