Palladium (IV) oxide

Crystal structure
__ Pd 4+      __ O 2−
General
Surname	Palladium (IV) oxide
other names	Palladium dioxide
Ratio formula	PdO 2
Brief description	dark red or black solid
External identifiers / databases
CAS number 12036-04-3 EC number 234-836-4 ECHA InfoCard 100,031,657 Wikidata Q2047953
properties
Molar mass	138.42 g mol −1
Physical state	firmly
Melting point	200 ° C (decomposes to PdO )
solubility	insoluble in water, acids and alkalis
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 272-413 P: ?
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Palladium (IV) oxide , also known as palladium dioxide , is a chemical compound of the elements palladium and oxygen . The oxide is dark red as a hydrate, while anhydrous is black, and at 200 ° C it breaks down into palladium (II) oxide .

Extraction and presentation

Palladium (IV) oxide is a precipitate when PdCl ₆ ²⁻ -containing aqueous solutions are mixed with dilute sodium hydroxide :

${\displaystyle \mathrm {Na_{2}PdCl_{6}+4\ NaOH\longrightarrow \ PdO_{2}+6\ NaCl+2\ H_{2}O} }$

A solution of sodium carbonate contains sufficient hydroxide ions and can be used instead of sodium hydroxide solution:

${\displaystyle \mathrm {Na_{2}PdCl_{6}+2\ Na_{2}CO_{3}\longrightarrow \ PdO_{2}+6\ NaCl+2\ CO_{2}\uparrow } }$

Another synthesis method is the anodic oxidation of palladium (II) nitrate . The production by oxidation of palladium (II) chloride with ozone proceeds with poor yields, since the palladium dioxide partially reacts further with the hydrochloric acid obtained as a by-product .

properties

Physical Properties

Palladium dioxide crystallizes in the tetragonal crystal system in the space group P 4 ₂ / mnm (space group no. 136) with the lattice parameters a = 448  pm and c = 310 pm as well as two formula units per unit cell ( rutile structure ).

Chemical properties

When heated, palladium dioxide gives off oxygen and changes to palladium (II) oxide at 200 ° C, which in turn breaks down into the elements at 875 ° C.

${\displaystyle \mathrm {2\ PdO_{2}\ \ {\xrightarrow[{-O_{2}}]{200^{\circ }C}}\ \ 2\ PdO\ \ {\xrightarrow[{-O_{2}}]{875^{\circ }C}}\ \ 2\ Pd} }$

The hydrate dissolves in concentrated sodium hydroxide solution with the formation of hexahydroxopalladate ions, the anhydrous substance is insoluble in alkalis.

${\displaystyle \mathrm {PdO_{2}+2\ NaOH+2\ H_{2}O\longrightarrow Na_{2}[Pd(OH)_{6}]} }$

The hydrate of palladium dioxide is also soluble in hydrochloric acid, and hexachloropalladate (IV) ions are formed in the process.

${\displaystyle \mathrm {PdO_{2}+6\ HCl\longrightarrow H_{2}[PdCl_{6}]+2\ H_{2}O} }$

Palladium dioxide is initially soluble in oxalic acid , turning yellow and forming dioxalatopalladate (II) ions [Pd (OOC-COO) ₂ ] ²⁻ ; when boiled, it is reduced to elemental palladium.

${\displaystyle \mathrm {PdO_{2}+2\ (COOH)_{2}\longrightarrow Pd+4\ CO_{2}\uparrow +2\ H_{2}O} }$

Elemental palladium is also formed when cooking with acetic acid .

Individual evidence

1. ↑ ^{a b} Palladium (IV) oxide on webelements.com
2. ^ ^{A b} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , p. 1732.
3. ↑ There is not yet a harmonized classification for this substance . A labeling of palladium dioxide in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), which was retrieved on July 10, 2020, is reproduced from a self-classification by the distributor .
4. ↑ ^{a b c d e} Lothar Wöhler, James König: "Die Oxyde des Palladiums" in Zeitschr. f. Anorg. Chem. 1905 , 46 , p. 323ff. ( Full text ).
5. ↑ IS Shaplygin, GL Aparnikov, VB Lazarev: Preparation of palladium dioxide at high pressure. In: Zhurnal Neorganicheskoi Khimii. 1978, 23, 4, pp. 884-887.
6. ^ ^{A b c} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 1520.
7. ^ MM Vezes: "Sur les sels complexes de palladium: palladoxalate" in Bull. Soc. Chim. 1899 , (3) 21 , pp. 172f. ( Full text ).