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Zeise's salt, potassium trichloro(ethylene)platinate(II), is the

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

with the

formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwe ...

K PtCl₃(C₂H₄).html" ;"title="platinum.html" ;"title="/nowiki>

PtCl₃(C₂H₄)">platinum.html"_;"title="/nowiki>platinum">PtCl₃(C₂H₄)�H₂O.__The_anion_of_this_air-stable,_yellow,_ PtCl₃(C₂H₄)">platinum.html"_;"title="/nowiki>platinum">PtCl₃(C₂H₄)�H₂O.__The_anion_of_this_air-stable,_yellow,_Complex_(chemistry)">coordination_complex_ A_coordination_complex_consists_of_a_central__atom_or__ion,_which_is_usually_metallic_and_is_called_the_''coordination_centre'',_and_a_surrounding_array_of__bound__molecules_or_ions,_that_are_in_turn_known_as_''_ligands''_or_complexing_agents.__M_...

_contains_an_hapticity.html" ;"title="Complex_(chemistry).html" "title="platinum">PtCl₃(C₂H₄)">platinum.html" ;"title="/nowiki>platinum">PtCl₃(C₂H₄)�H₂O. The anion of this air-stable, yellow, Complex (chemistry)">coordination complex A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as '' ligands'' or complexing agents. M ...

contains an hapticity">''η''²-

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...

ligand. The anion features a platinum atom with a square planar geometry. The salt is of historical importance in the area of

organometallic chemistry Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and s ...

as one of the first examples of a

transition metal alkene complex In organometallic chemistry, a transition metal alkene complex is a coordination compound containing one or more alkene ligands. Such compounds are intermediates in many catalytic reactions that convert alkenes to other organic products.Elschenbro ...

and is named for its discoverer,

William Christopher Zeise William Christopher Zeise (15 October 1789 – 12 November 1847) was a Danish organic chemist. He is best known for synthesising one of the first organometallic compounds, named Zeise's salt in his honour. He also performed pioneering studi ...

.

Preparation

This compound is commercially available as a hydrate. The hydrate is commonly prepared from K₂ tCl₄and

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...

in the presence of a

catalytic Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

amount of SnCl₂. The water of hydration can be removed ''in vacuo''.

Structure

The alkene C=C bond is approximately perpendicular to the PtCl₃ plane. In Zeise's salt and related compounds, the alkene rotates about the metal-alkene bond with a modest

activation energy In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules p ...

. Analysis of the barrier heights indicates that the π-bonding between most metals and the alkene is weaker than the σ-bonding. In Zeise's anion, this rotational barrier has not been assessed.

History

Zeise's salt was one of the first

organometallic Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and s ...

compounds to be reported. It was discovered by

William Christopher Zeise William Christopher Zeise (15 October 1789 – 12 November 1847) was a Danish organic chemist. He is best known for synthesising one of the first organometallic compounds, named Zeise's salt in his honour. He also performed pioneering studi ...

, a professor at the

University of Copenhagen The University of Copenhagen ( da, Københavns Universitet, KU) is a prestigious public university, public research university in Copenhagen, Copenhagen, Denmark. Founded in 1479, the University of Copenhagen is the second-oldest university in ...

, who prepared this compound in 1830 while investigating the reaction of PtCl₄ with boiling

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

. Following careful analysis he proposed that the resulting compound contained

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...

.

Justus von Liebig Justus Freiherr von Liebig (12 May 1803 – 20 April 1873) was a German scientist who made major contributions to agricultural and biological chemistry, and is considered one of the principal founders of organic chemistry. As a professor at th ...

, a highly influential chemist of that era, often criticised Zeise's proposal, but Zeise's proposal was decisively supported in 1868 when Birnbaum prepared the complex using ethylene. Zeise's salt received a great deal of attention during the second half of the 19th century because chemists could not explain its molecular structure. This question remained unanswered until the determination of its X-ray crystal structure in the 20th century. Zeise's salt stimulated much scientific research in the field of

organometallic chemistry Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and s ...

and would be key in defining new concepts in chemistry. The Dewar–Chatt–Duncanson model explains how the metal is coordinated to the C=C double bond.

Related compounds

* Zeise's dimer, ''η''²-C₂H₄)PtCl₂sub>2, derived from Zeise's salt by elimination of KCl followed by dimerisation. * COD-platinum dichloride, (cyclooctadiene)PtCl₂, derived from platinum(II) chloride and

1,5-cyclooctadiene Cycloocta-1,5-diene is a cyclic hydrocarbon with the chemical formula , specifically . There are three configurational isomers with this structure, that differ by the arrangement of the four C–C single bonds adjacent to the double bonds. Eac ...

, is a common platinum(II) alkene complex. Many other ethylene complexes have been prepared. For example, ethylenebis(triphenylphosphine)platinum(0), C₆H₅)₃Psub>2Pt(H₂C=CH₂), wherein the platinum is three-coordinate and in

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...

0 (Zeise's salt is a derivative of platinum(II)). * Dichloro(ethylene)(α- methylbenzylamine)platinum(II) (PtCl₂(C₂H₄)(PhCH(NH₂)Me) is a chiral derivative of Zeise's salt that is used for the

optical resolution Optical resolution describes the ability of an imaging system to resolve detail, in the object that is being imaged. An imaging system may have many individual components, including one or more lenses, and/or recording and display components. ...

of alkenes.

References

{{Platinum compounds Organoplatinum compounds Alkene complexes Chlorides Chloro complexes