Zeise's salt
Encyclopedia
Zeise's salt, potassium trichloro(ethene)platinate(II), is the chemical compound
with the formula
K[ Pt
Cl3(C2H4)]·H2O. The anion of this air-stable, yellow, coordination complex
contains an η2-ethylene
ligand
. The anion features a platinum atom with a square planar
geometry.
in the presence of a catalytic amount of SnCl2
. The water of hydration can be removed in vacuo.
. 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 cannot be assessed by NMR spectroscopy
because all four protons are equivalent. Lower symmetry complexes of ethylene, e.g. Cp
Rh(C2H4)2, are, however, suitable for analysis of the rotational barriers associated with the metal-ethylene bond.
compounds to be reported. Its inventor W. C. Zeise
, a professor at the University of Copenhagen
, prepared this compound in 1820s while investigating the reaction of PtCl4 with boiling ethanol
, and proposed that the resulting compound contained ethylene
. Justus von Liebig
, an influential chemist of that era, often criticised Zeise's proposal, but Zeise's theories were 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 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 much scientific research in the field of organometallic chemistry
, and would be key in defining new concepts in chemistry such as Hapticity
. The Dewar-Chatt-Duncanson model
explains how the metal is coordinated to the double bond.
Many other ethylene complexes have been prepared. For example, ethylenebis(triphenylphosphine)platinum(0), [(C6H5)3P]2Pt(H2C=CH2), wherein the platinum is three-coordinate and zero-valent (Zeise's salt is a derivative of platinum(II)).
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
K
Platinum
Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...
Cl3(C2H4)]·H2O. The anion of this air-stable, yellow, coordination complex
Complex (chemistry)
In chemistry, a coordination complex or metal complex, is an atom or ion , bonded to a surrounding array of molecules or anions, that are in turn known as ligands or complexing agents...
contains an η2-ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...
ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
. The anion features a platinum atom with a square planar
Square planar
The square planar molecular geometry in chemistry describes the stereochemistry that is adopted by certain chemical compounds...
geometry.
Preparation
This compound is commercially available as a hydrate. The hydrate is commonly prepared from K2[PtCl4] and ethyleneEthylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...
in the presence of a catalytic amount of SnCl2
Tin(II) chloride
Tin chloride is a white crystalline solid with the formula 2. It forms a stable dihydrate, but aqueous solutions tend to undergo hydrolysis, particularly if hot. SnCl2 is widely used as a reducing agent , and in electrolytic baths for tin-plating...
. The water of hydration can be removed in vacuo.
Structure
In Zeise's salt and related compounds, the alkene rotates about the metal-alkene bond with a modest activation energyActivation energy
In chemistry, activation energy is a term introduced in 1889 by the Swedish scientist Svante Arrhenius that is defined as the energy that must be overcome in order for a chemical reaction to occur. Activation energy may also be defined as the minimum energy required to start a chemical reaction...
. 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 cannot be assessed by NMR spectroscopy
NMR spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a research technique that exploits the magnetic properties of certain atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained...
because all four protons are equivalent. Lower symmetry complexes of ethylene, e.g. Cp
Cyclopentadienyl
In organic chemistry, cyclopentadienyl is a cyclic group of atoms with the formula C5H5. Cyclopentadienyl are closely related to cyclopentadiene. Cyclopentadienyl have five carbon atoms bonded together in a pentagonal planar ring, all five of which are bonded to individual hydrogen atoms...
Rh(C2H4)2, are, however, suitable for analysis of the rotational barriers associated with the metal-ethylene bond.
History
Zeise's salt was one of the first organometallicOrganometallic chemistry
Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
compounds to be reported. Its inventor W. C. Zeise
William Christopher Zeise
William Christopher Zeise was a Danish organic chemist. He is best known for the first organometallic compound to be synthesized, named Zeise's salt in his honor. He also discovered the xanthates in 1823....
, a professor at the University of Copenhagen
University of Copenhagen
The University of Copenhagen is the oldest and largest university and research institution in Denmark. Founded in 1479, it has more than 37,000 students, the majority of whom are female , and more than 7,000 employees. The university has several campuses located in and around Copenhagen, with the...
, prepared this compound in 1820s while investigating the reaction of PtCl4 with boiling ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
, and proposed that the resulting compound contained ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...
. Justus von Liebig
Justus von Liebig
Justus von Liebig was a German chemist who made major contributions to agricultural and biological chemistry, and worked on the organization of organic chemistry. As a professor, he devised the modern laboratory-oriented teaching method, and for such innovations, he is regarded as one of the...
, an influential chemist of that era, often criticised Zeise's proposal, but Zeise's theories were 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 properly explain the molecular structure
Molecular structure
The molecular structure of a substance is described by the combination of nuclei and electrons that comprise its constitute molecules. This includes the molecular geometry , the electronic properties of the...
of the salt. This question remained unanswered until the advent of x-ray diffraction in the 20th century.
Zeise's salt stimulated much scientific research in the field of organometallic chemistry
Organometallic chemistry
Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. Since many compounds without such bonds are chemically similar, an alternative may be compounds containing metal-element bonds of a largely covalent character...
, and would be key in defining new concepts in chemistry such as Hapticity
Hapticity
The term hapticity is used to describe how a group of contiguous atoms of a ligand are coordinated to a central atom. Hapticity of a ligand is indicated by the Greek character 'eta', η. A superscripted number following the η denotes the number of contiguous atoms of the ligand that are bound to...
. The Dewar-Chatt-Duncanson model
Dewar-Chatt-Duncanson model
The Dewar–Chatt–Duncanson model is a model in organometallic chemistry which explains the type of chemical bonding between an alkene and a metal in certain organometallic compounds. The model is named after Michael J. S. Dewar, Joseph Chatt and L. A...
explains how the metal is coordinated to the double bond.
Related compounds
- Zeise's dimer [{(η2-C2H4)PtCl2}2], derived from Zeise's salt by elimination of KCl followed by dimerisation.
- "COD-platinum dichloride," (cyclooctadiene)PtCl2, derived from platinum(II) chloridePlatinum(II) chloridePlatinum chloride is the chemical compound PtCl2. It is an important precursor used in the preparation of other platinum compounds. It exists in two crystalline forms, but the main properties are somewhat similar: dark brown, insoluble in water, diamagnetic, and odorless.-Structure:The...
and 1,5-cyclooctadiene1,5-Cyclooctadiene1,5-Cyclooctadiene is the organic compound with the chemical formula C8H12. Generally abbreviated COD, this diene is a useful precursor to other organic compounds and serves as a ligand in organometallic chemistry.- Synthesis :...
, is a common platinum(II) alkene complex.
Many other ethylene complexes have been prepared. For example, ethylenebis(triphenylphosphine)platinum(0), [(C6H5)3P]2Pt(H2C=CH2), wherein the platinum is three-coordinate and zero-valent (Zeise's salt is a derivative of platinum(II)).