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Dihydrogen hexachloroplatinate (IV) hexahydrate



Dihydrogen hexachloroplatinate (IV) hexahydrate
IUPAC name Dihydrogen hexachloroplatinate (IV)
hexahydrate
Other names Chloroplatinic Acid
Identifiers
CAS number 16941-12-1
RTECS number TP1510000
Properties
Molecular formula H2PtCl6•(H2O)6
Molar mass 517.891 g/mol
Appearance Reddish brown solid
Density 2.431 g/cm³, solid
Melting point

60 °C (333 K)

Boiling point

decomp

Solubility in water highly sol
Structure
Crystal structure Anti-fluorite.
Coordination
geometry
octahedral
Dipole moment 0 D
Hazards
MSDS External MSDS
NFPA 704
0
3
0
 
R-phrases R34, R42, R43
S-phrases S22, S26, S36, S37, S39, S45
Related Compounds
Other anions H2PdCl6 (unstable) hexachloropalladic Acid
Other cations K2PtCl6 Potassium Chloroplatinate
K2PtCl4 Potassium Tetrachloroplatinate
(NH4)2PtCl6 Ammonium Chloroplatinate,
Rb2PtCl6 Rubidium Chloroplatinate,
Cs2PtCl6 Cæsium Chloroplatinate
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references


Dihydrogen hexachloroplatinate (IV) hexahydrate is the chemical compound with the formula H2PtCl6•(H2O)6). Also known as hexachlorplatinic acid or chloroplatinic acid, is one of the most readily available soluble compounds of platinum, but it is also unusual in that it is rarely obtained in a highly pure state. The commercial product is the oxonium salt of the hexachloroplatinate(IV) anion. Therefore, the correct formula is [H3O]2[PtCl6]•4H2O.(5,6) The related palladium compound,[H3O]2[PdCl6] is extremely unstable and has not been isolated in pure form.[1]

Additional recommended knowledge

Contents

Use in determination of potassium

Chloroplatinic acid was popularlized for the determination of potassium. The potassium is selectively precipitated as potassium chloroplatinate. Determinations were done in 85% (v/v) alcohol solutions with excess platinate ions, and the precipitated product was weighed. Potassium could be detected for solutions as dilute as 0.02 to 0.2% (m/v).[2]

This method for determination of potassium was advantageous vs. the cobaltinitrite method used previously, since it required a single precipitation reaction.[citation needed] Today, the concentration of potassium is determined with an ion-selective electrode. These modern methods remain subject to interference.

Production

Chloroplatinic acid is produced by dissolving platinum metal sponge in a 1:4 (v:v) solution of nitric acid and hydrochloric acid called aqua regia. This reaction is rumored to produce nitrogen-containing platinum compounds, but the product is H2PtCl6. Chloroplatinic acid is brownish-red, and can be isolated by evaporating this solution to a syrup.[3]

Pt + 4 HNO3 + 6 HCl → H2PtCl6 + 4 NO2 + 4 H2O

Alternative methods have been heavily investigated, but the older literature can be unreliable.[4]

Chemical properties

Like many platinum compounds, chloroplatinic acid is used in catalysis. This compound was first used by John Speier and his colleagues from Dow Corning Corporation to catalyze the reaction of silyl hydrides with olefins.(3) Typical of his reactions, Speier used isopropanol solutions containing trichlorosilane (SiHCl3), and methyldichlorosilane (CH3HSiCl2), with pentenes. Speier found that chloroplatinic acid avoided polymerization, a problem that plagued previous attempts at hydrosilylation.



Much speculation has surrounded the actual site of catalysis in chloroplatinic acid. Speier himself proposed that catalysis centered on the platinate ion, and possibly involved an oxidative addition reductive elimination process with the olefinic substrate.[5][6] This process seems plausible since the chlorine ligands of the complex would be labile.

However, more recent evidence has suggested that catalysis with chloroplatinic acid involves low valent platinum. The II and IV oxidation states of platinum could not afford the highly catalytic nature of the reactions observed. Lewis and his coworkers have suggested a mechanism involving Pt(0) with olefins as ligands.[7]


Related compounds

Chloroplatinic acid is occasionally contaminated with (NO)2PtCl6, and this problem has been the source of considerable discussion. This species is obtained by the reaction of nitrosyl chloride and Pt metal.[8]

References

  1. ^ Earnshaw, Greenwood, N. N. Chemistry of the Elements. Second Edition. Elsevier Butterworth-Heinemann. New York. 2005.
  2. ^ G. F. Smith, J. L. Gring (1933). "The Separation and Determination of the Alkali Metals Using Perchloric Acid. V. Perchloric Acid and Chloroplatinic Acid in the Determination of Small Amounts of Potassium in the Presence of Large Amounts of Sodium". J. Am. Chem. Soc. 55 (10): 3957-3961. doi:10.1021/ja01337a007.
  3. ^ Kauffman, G. B. "Ammonium Hexachloroplatinate" Inorganic Syntheses McGraw-Hill: New York, 1967, IX, pages 182-4.
  4. ^ Rudnick, P.; Cooke, R. D. "THE PREPARATION OF HYDROCHLOROPLATINIC ACID BY MEANS OF HYDROGEN PEROXIDE" Journal of the American Chemical Society 1917, volume 39, pages 633-635.
  5. ^ J. L. Speier, J. A. Webster, G. H. Barnes "The Addition of Silicon Hydrides to Olefinic Double Bonds. Part II. The Use of Group VIII Metal Catalysts" J. Am. Chem. Soc.; 1957; 79(4); 974-979.
  6. ^ John C. Saam, John L. Speier. "The Addition of Silicon Hydrides to Olefinic Double Bonds. Part 111. The Addition to Non-terminal Olefins in the Presence of Chloroplatinic Acid" Journal of the American Chemical Society 1958, volume 80, page 4104.
  7. ^ L.N. Lewis, K.G. Sy, G.L. Bryant, Jr. and P.E. Donahue. Organometallics 10 (1991), p. 3750.
  8. ^ Moravek, R. T.; Kauffman, G. T. "Nitrosyl Hexachloroplatinate" Inorganic Syntheses, 1986, volume 24, p 217-219. ISBN 0-471-83441-6

Other reading

  • Schweizer, G. T. Kerr. Thermal Decomposition of Hexachloroplatinic Acid. Inorg. Chem.; 1978; 17(8); 2326-2327.
  • Holleman, Wiberg. Inorganic Chemistry First Edition. Academic Press. New York, 2001
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Dihydrogen_hexachloroplatinate_(IV)_hexahydrate". A list of authors is available in Wikipedia.
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