Platinum(II) chloride

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Platinum(II) chloride
Platinum(II) chloride
Identifiers
CAS number 10025-65-7 N
PubChem 2770
ChemSpider 2668 YesY
ChEBI CHEBI:49801 YesY
Jmol-3D images Image 1
Properties
Molecular formula PtCl2
Molar mass 265.99 g/mol
Appearance olive green crystals
Density 6.05 g/cm3, solid
Melting point 581 °C
Boiling point decomposes
Solubility in water insoluble
Solubility insoluble in alcohol, ether
soluble in HCl, ammonia
Structure
Crystal structure hexagonal
Hazards
EU classification not listed
LD50 3423 mg/kg (rat, oral)
Related compounds
Other anions platinum(II) sulfide, platinum(II) iodide
Other cations palladium(II) chloride, iridium dichloride
Related compounds platinum trichloride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Platinum(II) 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[edit]

The structures of PtCl2 and PdCl2 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 ligands. Complementarily, each Cl center is two-coordinate, being connected to two platinum atoms.[1]

Evolution of β-PtCl2 structure: Start with cubic lattice, remove corner and centered lattice points, inscribe octahedron (red lines), label corners as X (twelve Cl centers) and face-centered atoms as M (six Pt(II) centers).

Preparation[edit]

β-PtCl2 is prepared by heating chloroplatinic acid to 350 °C in air.[2]

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 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:[3]

PtCl4 → PtCl2 + Cl2

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.

Uses[edit]

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 that have been described, the following are illustrative:[4]

  • pink K2PtCl4, a widely employed water-soluble derivative.
  • colorless cis-PtCl2(NH3)2, better known as cisplatin.
  • colorless cis-PtCl2(P(C6H5)3)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- isomer.
  • colorless dichloro(cycloocta-1,5-diene)platinum(II) (Pt(cod)Cl2), an "organic-soluble" compound containing a labile organic ligand.

Several of these compounds are of interest in homogeneous catalysis in the service of organic synthesis or as anti-cancer drugs.

See also[edit]

References[edit]

  1. ^ Holleman, A. F.; Wiberg, E. Inorganic Chemistry Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
  2. ^ Kerr, G. T.; Schweizer, A. E. (1980). "β-Platinum(II) Chloride". Inorg. Synth. Inorganic Syntheses 20: 48–49. doi:10.1002/9780470132517.ch14. ISBN 978-0-470-13251-7. 
  3. ^ Wöhler, L.; Streicher, S. (1913). "Über das Beständigkeitsgebiet von vier wasserfreien Platinchloriden, über die Flüchtigkeit des Metalls im Chlorgas und die Darstellung sauerstoff-freien Chlors". Chem. Ber. 46 (2): 1591–1597. doi:10.1002/cber.19130460252. 
  4. ^ Cotton, S. A. Chemistry of Precious Metals, Chapman and Hall (London): 1997. ISBN 0-7514-0413-6