Platinum(II) chloride describes the

inorganic compound An inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds⁠that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as ''inorganic chemistry''. Inorgan ...

s with the formula Pt Cl₂. They are precursor used in the preparation of other platinum compounds. Platinum(II) chloride exists in two crystalline forms ( polymorphs), but the main properties are somewhat similar: dark brown, insoluble in water,

diamagnetic Diamagnetism is the property of materials that are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagn ...

, and odorless.

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

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

s. Complementarily, each Cl center is two-coordinate, being connected to two platinum atoms. The structure of α-PtCl₂ is reported to be disordered and contain edge- and/or corner-sharing square-planar PtCl₄ units. Beta-PdCl2

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 Hydrazinium is the cation with the formula . This cation has a methylamine-like structure (). It can be derived from hydrazine by protonation (treatment with a strong acid). Hydrazinium is a weak acid with p''K''a = 8.1. Salts of hydrazinium ar ...

salts, but this method is more laborious than the thermal route of Kerr and Schweizer. Although PtCl₂ can form when platinum metal contacts hot

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

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: :PtCl₄ → PtCl₂ + Cl₂ Transformations such as this are "driven" by

entropy Entropy is a scientific concept, most commonly associated with states of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynamics, where it was first recognized, to the micros ...

, 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.

Reactions

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 Addition of ammonia gives initially "PtCl₂(NH₃)₂", " Magnus's green salt", also described as t(NH₃)₄PtCl₄]. Many complex (chemistry), complexes have been described, the following are illustrative:Cotton, S. A. ''Chemistry of Precious Metals'', Chapman and Hall (London): 1997. *pink K₂PtCl₄, a widely employed water-soluble derivative. *colorless ''cis''-PtCl₂(NH₃)₂, better known as

cisplatin Cisplatin is a chemical compound with chemical formula, formula ''cis''-. It is a coordination complex of platinum that is used as a chemotherapy medication used to treat a number of cancers. These include testicular cancer, ovarian cancer, c ...

. *colorless ''cis''-PtCl₂(P(C₆H₅)₃)₂, a common precursor to 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 In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

. *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 chemistry, homogeneous catalysis is catalysis where the catalyst is in same phase as reactants, principally by a soluble catalyst in a solution. In contrast, heterogeneous catalysis describes processes where the catalysts and substrate are in d ...

in the service of

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

or as anti-cancer drugs.

References

{{Chlorides Chlorides Chlorides,2 Platinum group halides

Structure

Preparation

Reactions

See also

References