PLATINUM(II) CHLORIDE

Platinum(II) chloride
Platinum(II) chloride
General
Other names	platinous chloride
Molecular formula	PtCl2
Molar mass	265.99 g/mol
Appearance hexagonal form	brown odorless powder
CAS number	[10025-65-7]
Properties
Density and phase	6.05 g/cm3, solid
Solubility in water	insoluble
Melting point	581 °C
Boiling point	decomposes
'Hazards'
EU classification	not listed
NFPA 704
Related compounds
Related compounds	PtCl4 H2PtCl6 K2PtCl6 K2PtCl4
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)

'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.

Contents

Structure

Preparation

Uses

References

External links

Structure

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]

Preparation

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

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' 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 PtCl₂(cyclooctadiene), 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.

References

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. ''Inorganic Syntheses'' 1980, volume XX, pages 48-49. ISBN 0-471-07715-1
3. Wöhler, L.; Streicher, S. ''Chemische Berichte,'' 1913, volume 46, page 1591ff.
4. Cotton, S. A. "Chemistry of Precious Metals," Chapman and Hall (London): 1997. ISBN 0-7514-0413-6

External links