Synthesis of mixed-ligand complexes by co-proportionation

In preparative coordination diemistry mixed-ligand complexes are often prepared by co-proportionation of homoleptic complexes. The reaction between K2[Pt(NC 2)4] and K2[PtBr4] is representative/ Eq. 1.4  

If the amine ligands present in the two reactants are different, then the preparation of platinum(II) complexes with four different ligands becomes possible. Octahedral platinum(IV) complexes with six different ligands are also well known and syntheses of such compounds can be designed only when the trans-effects of the individual ligands are taken into account (see Section 1.4). 

In 1920, based on relatively few experimental data (only about 10 reactions were known), Chugaev concluded that Magnus salts, [PtL4][PtX4] (X = Cl, Br L = amines, thioethers), were subject to solid-state rearrangement upon heating, Eq. 1.6  

The formation of mixed-ligand complexes by co-proportionation of homoleptic complexes has been considered theoretically. The crucial issue is 

Equation 1.8 suggests that the co-proportionation constant, calculated on a statistical basis, will always be above unity. Thus, the statistical redistribution of ligands will favor the formation of mixed-ligand complexes. 

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