Zeise's salt

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Zeise's salt is an air-stable, yellow, crystalline compound of platinum and ethylene, with the chemical formula K[PtCl₃(η²-C₂H₄)].H₂O. It is commonly made from K₂[PtCl₄] and free ethylene with some SnCl₂ as a catalyst.

Contents 1 History 1.1 Bonding 2 Related compounds 3 External links 4 References

[edit] History

Zeise's salt was one of the first organometallic compounds to be synthesized. Its inventor W. C. Zeise made it in 1827 when he boiled PtCl₄ in ethanol, and he proposed that the resulting compound contained ethylene. Justus von Liebig often criticised Zeise's proposal but Liebig's theories were finally dismissed by Birnbaum in 1868 when he proved the presence of ethylene.

Zeise's salt received a great deal of attention during the second half of the 19th century because chemists could not properly explain the molecular structure of the salt. This question remained unanswered until the advent of x-ray diffraction in the 20th century.

Zeise's salt stimulated the scientific research in organomatellic field, and would come to be the keystone of new terms to come in chemistry such as "Hapticity".^[1]

[edit] Bonding

The metal-alkene bonding is a classic example of the Dewar-Chatt-Duncanson model of synergic bonding between a ligand and a metal. The alkene donates electron density into a metal d-orbital from carbon-carbon π-symmetry bonding orbital, and the metal donates it back from (a different) d-orbital into the carbon-carbon π^* orbital. Both of these effects tend to reduce the carbon-carbon bond order from 2 to 1, making this bond longer and lowering its vibrational frequency. They also move the hybridisation at the carbon atoms from sp² towards sp³, which has the effect of making the protons on the ethylene bend back away from the metal.

In both of these compounds the alkene is free to rotate about the metal-alkene bond at higher temperatures. However, at lower temperatures the alkene is static, and is perpendicular to the square plane about the platinum atom (as in the picture above!).

[edit] Related compounds

• Ethylenebis(triphenylphosphine)platinum(0) [(C₆H₅)₃P]₂Pt(H2C=CH2), where the chloride ligands of the Zeise's salt have been replaced by two triphenylphosphine ligands.
• Zeise's dimer [{(η²-C₂H₄)PtCl₂}₂], essentially Zeise's salt that has lost KCl and dimerised.

[edit] External links

• Datasheet [(C₆H₅)₃P]₂Pt(H2C=CH2)Link
• Links to external chemical sources.

[edit] References

• ↑ Miessler, Gary L., Donald A. Tarr (2004). Inorganic Chemistry. Upper Saddle River, New Jersey: Pearson Education, Inc. Pearson Prentice Hall. ISBN 0-13-035471-6.