Palladium(II) oxide

Palladium(II) oxide
Names
	Other names Palladium monoxide
Identifiers
CAS Number	1314-08-5 ;
3D model (JSmol)	Interactive image;
ChemSpider	66602 ;
ECHA InfoCard	100.013.836
PubChem CID	73974;
UNII	B30901Q32J ;
CompTox Dashboard (EPA)	DTXSID90894899 ;
	InChI InChI=1S/O.Pd/q-2;+2 Key: JQPTYAILLJKUCY-UHFFFAOYSA-N ; InChI=1/O.Pd/q-2;+2 Key: JQPTYAILLJKUCY-UHFFFAOYAD;
	SMILES [Pd+2].[O-2];
Properties
Chemical formula	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
Solubility in water	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). verify (what is ?) Infobox references

Palladium(II) oxide is the inorganic compound of formula Pd O. 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

^ ^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.
^ 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.
^ ^a ^b Donald Starr and R. M. Hixon (1943). "Tetrahydrofuran". Organic Syntheses; Collected Volumes, vol. 2, p. 566.
^ Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1965, NY. Vol. 2. p. 1583.

[Greenwood-1] 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.

[OS-3] 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.

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