Ammonium hexachloropalladate(IV)
[CAS# 19168-23-1]

Identification

• Classification: Organic raw materials >> Organometallic compound >> Organic palladium
• Name: Ammonium hexachloropalladate(IV)
• Synonyms: Diammonium hexachloropalladate; Palladium(IV)-ammonium chloride
• Molecular Formula: (NH₄)₂.PdCl₆
• Molecular Weight: 355.21
• CAS Registry Number: 19168-23-1
• EC Number: 242-854-9
• SMILES: [NH4+].[NH4+].Cl[Pd-2](Cl)(Cl)(Cl)(Cl)Cl

Properties

• Water solubility: slightly soluble

Safety Data

• Hazard Symbols: GHS05;GHS06;GHS07;GHS09 Danger
• Risk Statements: H301-H302-H315-H317-H318-H319-H400-H410
• Safety Statements: P261-P264-P264+P265-P270-P272-P273-P280-P301+P316-P301+P317-P302+P352-P305+P351+P338-P305+P354+P338-P317-P321-P330-P332+P317-P333+P317-P337+P317-P362+P364-P391-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Serious eye damage	Eye Dam.	1	H318
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Acute toxicity	Acute Tox.	3	H301
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Skin sensitization	Skin Sens.	1A	H317
Acute toxicity	Acute Tox.	4	H302
Eye irritation	Eye Irrit.	2	H319

Discovery and Applications

Ammonium hexachloropalladate(IV), with the chemical formula (NH₄)₂[PdCl₆], is an inorganic coordination compound consisting of the hexachloropalladate(IV) anion [PdCl₆]²⁻ and two ammonium cations (NH₄⁺). It is a well-defined salt characterized by the palladium ion in the +4 oxidation state, coordinated octahedrally by six chloride ligands, forming a stable complex anion. The compound typically appears as yellow crystalline solids that are soluble in water and certain polar solvents.

The synthesis of ammonium hexachloropalladate(IV) generally involves the oxidation of palladium metal or palladium(II) salts in the presence of hydrochloric acid and ammonium salts under strongly oxidizing conditions. The palladium is converted to the +4 oxidation state, and the hexachloropalladate complex forms through coordination with chloride ions in solution. Crystallization from the aqueous medium affords the ammonium salt as solid crystals.

Structurally, the hexachloropalladate(IV) ion adopts an octahedral geometry with palladium(IV) at the center bound symmetrically to six chloride ions. This geometry is typical for d⁶ transition metal complexes in the +4 oxidation state. The ammonium ions balance the charge and contribute to the compound's high aqueous solubility.

Ammonium hexachloropalladate(IV) serves as a key intermediate and precursor in palladium chemistry, particularly in catalyst preparation. It is widely used in the synthesis of palladium-based catalysts employed in hydrogenation, carbon–carbon coupling reactions, and other organic transformations. Thermal decomposition of the compound yields palladium metal or palladium oxides, depending on conditions, making it valuable for producing finely divided palladium catalysts supported on various materials.

In materials science, the compound is used in the deposition of palladium thin films and nanoparticles through chemical vapor deposition and solution-based methods. Its stability and solubility allow for controlled palladium release during synthesis, facilitating precise material engineering.

Analytically, ammonium hexachloropalladate(IV) is employed in quantitative and qualitative analysis of palladium content, providing a well-characterized and pure source of palladium(IV) complexes. It also aids in studying the redox and coordination behavior of palladium in different chemical environments.

Handling ammonium hexachloropalladate(IV) requires caution, as it is an oxidizing agent and may pose health risks if inhaled, ingested, or upon skin contact. Protective measures include using gloves, goggles, and working in ventilated areas. It should be stored in a cool, dry place away from reducing agents and incompatible substances.

Thermally, the compound decomposes upon heating, releasing hydrogen chloride gas and leaving behind palladium residues. This property is exploited in catalyst preparation and metal recovery processes but requires controlled conditions to ensure safety.

In summary, ammonium hexachloropalladate(IV) is a yellow crystalline salt composed of the octahedral hexachloropalladate(IV) anion and ammonium cations. It plays an important role as a precursor in palladium catalyst synthesis, materials fabrication, and analytical chemistry. Its well-defined structure, aqueous solubility, and thermal behavior make it valuable in industrial and laboratory applications involving palladium chemistry.

References

1987. Platinum group metal sensitivity: reactivity to platinum group metal salts in platinum halide salt-sensitive workers. Annals of Allergy, 59(6).
URL: https://pubmed.ncbi.nlm.nih.gov/3122607

1979. Inhibition of creatine kinase activity and alterations in electrophoretic mobility by palladium ions. Journal of Environmental Pathology and Toxicology, 2(3).
URL: https://pubmed.ncbi.nlm.nih.gov/422942

1976. Inhibition of hydroxyproline synthesis by palladium ions. Biochimica et Biophysica Acta (BBA) - Enzymology, 428(2).
DOI: 10.1016/0005-2744(76)90030-9