Trans effect

The trans effect referred to in the complex chemistry of the effect of ligands on the rate of substitution of this trans-disposed ligands. The effect is well studied in square-planar complexes and is used for example for the preparation of cisplatin. The trans effect was discovered in 1926 by Ilya Tschernjajew.

Kinetic trans - Effect

The strength of the trans effect of a ligand is determined by the rate of substitution of this trans-disposed ligands and has the following sequence for simple complex ligands:

F-, H2O, OH - < NH3 < py < Cl - < Br - < I-, SCN -, NO2 -, SC (NH2 ) 2, Ph- < SO32 - < PR3, AsR3, SR2, CH3 < H-, NO, CO, CN, C2H4

A well-known example of the use of the trans effect is the appearance of cisplatin. Starting from tetrachloroplatinate (II ), by reaction with ammonia in the first step the Monoammin complex. Due to the stronger trans -directing properties of chlorido ligands compared to the ammine ligands a second ammonia molecule trans to be installed at a chlorido ligands and thus in cis to the first ammine ligands:

If we contrast tetraamminepalladium complex and exchanges the ammine ligands against a chlorido ligands, the first built chlorido ligand directs the second in the trans position to the first. Is obtained in this case transplatin:

The trans effect can be explained by the σ-Donor/π-Akzeptor properties of the ligands. Good σ -donors and π - acceptors have a strong trans effect.

Thermodynamic trans influence

The trans influence referred to in the complex chemistry the thermodynamic effect of a ligand on the properties of the ground state ( bond length, IR spectrum ) to a trans-disposed ligands.

"The trans influence is defined as the extent to Which a ligand weakens a bond trans to it in the equilibrium state".