Palladium(II) oxide

Palladium(II) oxide
Names
Other names
Palladium monoxide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.013.836 Edit this at Wikidata
UNII
  • InChI=1S/O.Pd/q-2;+2 checkY
    Key: JQPTYAILLJKUCY-UHFFFAOYSA-N checkY
  • InChI=1/O.Pd/q-2;+2
    Key: JQPTYAILLJKUCY-UHFFFAOYAD
  • [Pd+2].[O-2]
Properties
PdO
Molar mass 122.42 g/mol
Appearance greenish-black powder
Density 8.3 g/cm3
Melting point 750 °C (1,380 °F; 1,020 K) decomposes
insoluble
Solubility insoluble in acid
slightly soluble in aqua regia
Hazards
Flash point Non-flammable
Related compounds
Other anions
 Palladium sulfide
Other cations
 Nickel(II) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Palladium(II) oxide is the inorganic compound of formula PdO. It is the only well characterised oxide of palladium.[1] It is prepared by treating the metal with oxygen. Above about 900 °C, the oxide reverts to palladium metal and oxygen gas. It is not attacked by acids.[1]

Structure

The structure of PdO is tetragonal (P42/mmc) a = 3.044, c = 5.328 Å. The Pd atoms are square planar as expected for a d8 metal ion and the oxygen atoms are approximately tetrahedral.[2] The closest Pd–Pd distance is 3.044 Å and is almost within the range which can be considered a bonding distance.

Preparation

PdO is often obtained as a poorly defined material that is generated for applications as a catalyst. Palladium oxide is prepared by heating palladium sponge metal in oxygen at 350 °C.

2 Pd + O2 → 2 PdO

The oxide is obtained as a black powder. The oxide also may be prepared specially for catalytic use by heating variously a mixture of palladium(II) chloride and potassium nitrate,

2 PdCl2 + 4 KNO3 → 2 PdO + 4 KCl + 4 NO2 + O2 (possible reaction)

or the product of dissolving palladium in aqua regia, followed by the addition of sodium nitrate at 600 °C.[3][4] A hydrated form of the oxide (which dissolves in acid) can be prepared by precipitation from solution, for example, by hydrolysis of palladium nitrate or reaction of a soluble palladium compound with a strong base. The brown hydrated oxide converts to black anhydrous oxide on heating. Its susceptibility to attack by acids decreases at lower water content.

The hydrated oxide, PdO.nH2O can be produced as a dark-yellow precipitate by adding alkali to a solution of palladium nitrate, Pd(NO3)2.[1]

Applications

Materials called palladium oxide are useful catalysts for catalytic hydrogenation in organic synthesis.[3]

References

  1. ^ a b c Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 1336–37. ISBN 978-0-08-022057-4.
  2. ^ Dwight, P.H. (1990). "Preparation and Properties of the System CuxPd1-xO (0<=x<=0.175)". J. Solid State Chem. 86: 175. doi:10.1016/0022-4596(90)90132-H.
  3. ^ a b Donald Starr and R. M. Hixon (1943). "Tetrahydrofuran". Organic Syntheses; Collected Volumes, vol. 2, p. 566.
  4. ^ Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1965, NY. Vol. 2. p. 1583.