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Platinum(II) chloride
Encyclopedia
Platinum chloride is the chemical compound
Pt
Cl2
. 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.
are similar. These dichlorides exist in both polymeric, or "α", and hexameric, or "β" structures. The β form converts to the α form at 500 °C. In the β form, the Pt-Pt distances are 3.32-3.40 Å, indicative of some bonding between the pairs of metals. In both forms of PtCl2, each Pt center is four-coordinate, being surrounded by four chloride ligand
s. Complementarily, each Cl center is two-coordinate, being connected to two platinum atoms.
This method is convenient since the chloroplatinic acid is generated readily from Pt metal. Aqueous solutions of H2PtCl6 can also be reduced with hydrazinium
salts, but this method is more laborious than the thermal route of Kerr and Schweizer.
Although PtCl2 must form when platinum metal contacts hot chlorine
gas, this process suffers from over-chlorination to give PtCl4
. Berzelius
and later Wöhler and Streicher showed that upon heating to 450 °C, this Pt(IV) compound decomposes to the Pt(II) derivative:
Transformations such as this are "driven" by entropy
, the free energy gained upon the release of a gaseous product from a solid. Upon heating to still higher temperatures, PtCl2 releases more chlorine to give metallic Pt. This conversion is the basis of the gravimetric assay of the purity of the PtCl2 product.
Sometimes, such reactions can be deceptive. Addition of ammonia gives initially "PtCl2(NH3)2", but this material is in fact Magnus's green salt, [PtCl4][Pt(NH3)4].
Of the many such complexes
that have been described, the following are illustrative:
Several of these compounds are of interest in homogeneous catalysis
in the service of organic synthesis
or as anti-cancer drugs.
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...
Pt
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...
Cl2
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
. 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
Diamagnetism
Diamagnetism is the property of an object which causes it to create a magnetic field in opposition to an externally applied magnetic field, thus causing a repulsive effect. Specifically, an external magnetic field alters the orbital velocity of electrons around their nuclei, thus changing the...
, and odorless.
Structure
The structures of PtCl2 and PdCl2Palladium(II) chloride
Palladium chloride, also known as palladium dichloride, are the chemical compounds with the formula PdCl2. PdCl2 is a common starting material in palladium chemistry – palladium-based catalysts are of particular value in organic synthesis. It is prepared by chlorination of...
are similar. These dichlorides exist in both polymeric, or "α", and hexameric, or "β" structures. The β form converts to the α form at 500 °C. In the β form, the Pt-Pt distances are 3.32-3.40 Å, indicative of some bonding between the pairs of metals. In both forms of PtCl2, each Pt center is four-coordinate, being surrounded by four chloride 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...
s. Complementarily, each Cl center is two-coordinate, being connected to two platinum atoms.
Preparation
β-PtCl2 is prepared by heating chloroplatinic acid to 350 °C in air.- H2PtCl6 → PtCl2 + Cl2 + 2 HCl
This method is convenient since the chloroplatinic acid is generated readily from Pt metal. Aqueous solutions of H2PtCl6 can also be reduced with hydrazinium
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
salts, but this method is more laborious than the thermal route of Kerr and Schweizer.
Although PtCl2 must form when platinum metal contacts hot chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
gas, this process suffers from over-chlorination to give PtCl4
Platinum(IV) chloride
Platinum chloride is the inorganic compound of platinum and chlorine with the empirical formula PtCl4. This brown solid features platinum in the 4+ oxidation state.-Structure:...
. Berzelius
Jöns Jakob Berzelius
Jöns Jacob Berzelius was a Swedish chemist. He worked out the modern technique of chemical formula notation, and is together with John Dalton, Antoine Lavoisier, and Robert Boyle considered a father of modern chemistry...
and later Wöhler and Streicher showed that upon heating to 450 °C, this Pt(IV) compound decomposes to the Pt(II) derivative:
- PtCl4 → PtCl2 + Cl2
Transformations such as this are "driven" by entropy
Entropy
Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process, such as in energy conversion devices, engines, or machines. Such devices can only be driven by convertible energy, and have a theoretical maximum efficiency when...
, the free energy gained upon the release of a gaseous product from a solid. Upon heating to still higher temperatures, PtCl2 releases more chlorine to give metallic Pt. This conversion is the basis of the gravimetric assay of the purity of the PtCl2 product.
Uses
Most reactions of PtCl2 proceed via treatment with ligands (L) to give molecular derivatives. These transformations entail depolymerization via cleavage of Pt-Cl-Pt linkages:- PtCl2 + 2 L → PtCl2L2
Sometimes, such reactions can be deceptive. Addition of ammonia gives initially "PtCl2(NH3)2", but this material is in fact Magnus's green salt, [PtCl4][Pt(NH3)4].
Of the many such complexes
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...
that have been described, the following are illustrative:
- pink K2PtCl4, a widely employed water-soluble derivative.
- colorless cis-PtCl2(NH3)2, better known as cisplatinCisplatinCisplatin, cisplatinum, or cis-diamminedichloroplatinum is a chemotherapy drug. It is used to treat various types of cancers, including sarcomas, some carcinomas , lymphomas, and germ cell tumors...
. - colorless cis-PtCl2(P(C6H5)3TriphenylphosphineTriphenylphosphine is a common organophosphorus compound with the formula P3 - often abbreviated to PPh3 or Ph3P. It is widely used in the synthesis of organic and organometallic compounds. PPh3 exists as relatively air stable, colorless crystals at room temperature...
)2, a commonly employed, easily crystallized species that is widely employed as a precursor other complexes of the type PtX(Cl)(P(C6H5)3)2 (X = H, CH3, etc.). - yellow trans-PtCl2(P(C6H5)3)2, a metastable relative of the cis- isomerIsomerIn chemistry, isomers are compounds with the same molecular formula but different structural formulas. Isomers do not necessarily share similar properties, unless they also have the same functional groups. There are many different classes of isomers, like stereoisomers, enantiomers, geometrical...
. - colorless dichloro(cycloocta-1,5-diene)platinum(II)Dichloro(cycloocta-1,5-diene)platinum(II)Dichloroplatinum is an organometallic compound of platinum. This colourless solid, which is a commercially available, is an entry point to other platinum compounds through the displacement of the cod and/or chloride ligands. It is prepared from potassium tetrachloroplatinate and the diene....
(Pt(cod)Cl2), an "organic-soluble" compound containing a labile organic ligand.
Several of these compounds are of interest in homogeneous catalysis
Homogeneous catalysis
In chemistry, homogeneous catalysis is a sequence of reactions that involve a catalyst in the same phase as the reactants. Most commonly, a homogeneous catalyst is codissolved in a solvent with the reactants.-Acid catalysis:...
in the service of organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
or as anti-cancer drugs.