trans effect

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In complex chemistry, the trans effect describes the effect of a ligand on the rate of substitution of a ligand in the trans position. The effect has been well investigated in square-planar complexes and is used, for example, to represent cisplatin . The trans effect was discovered by Ilya Chernyayev in 1926 .

Kinetic trans effect

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

F - , H 2 O , OH - < NH 3 < py < Cl - < Br - < I - , SCN - , NO 2 - , SC (NH 2 ) 2 , Ph - < SO 3 2− < PR 3 , AsR 3 , SR 2 , CH 3 - < H - , NO , CO , CN - , C 2 H 4

A well-known example of the use of the trans effect is the representation of cisplatin. Starting from tetrachloridoplatinate (II), the monoammine complex is obtained by reacting with ammonia in the first step. Due to the stronger trans -directing properties of the chlorido ligand compared to the ammine ligand, a second ammonia molecule is incorporated in the trans position to a chlorido ligand and thus in the cis position to the first ammine ligand:

Representation of cisplatin using the trans effect

If, on the other hand, one assumes the tetraammine complex and exchanges the ammine ligand for a chlorido ligand, the first incorporated chlorido ligand directs the second in trans position to the first. In this case transplatin is obtained :

Representation of transplatinum using the trans effect

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

Thermodynamic trans -Influence

In complex chemistry, the trans influence denotes the thermodynamic effect of a ligand on the properties of the ground state (bond length, IR spectrum) of a ligand in the trans position.

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

Transinfluence.png

Individual evidence

  1. ^ George B. Kauffman: The Izvestiya of the Platinum Institute. In: Platinum Metals Rev. 18, 1974, pp. 142-148. (PDF; 626 kB)
  2. ^ A. Pidcock, RE Richards, LM Venanzi: 195 Pt – 31P nuclear spin coupling constants and the nature of the trans-effect in platinum complexes. In: J. Chem. Soc. A 1966, pp. 1707-1710, doi : 10.1039 / J19660001707 .

literature

  • JE Huheey, Ellen Keiter, Richard L. Keiter: Inorganic Chemistry. Principles of structure and reactivity. Gruyter publishing house, Berlin 2003, ISBN 3-11-017903-2 .