Ammonium tetrachloropalladate
[CAS# 13820-40-1]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Inorganic ammonium salt
• Name: Ammonium tetrachloropalladate
• Synonyms: Palladium(II)-ammonium chloride; Ammonium tetrachloropalladate(II)
• Molecular Formula: (NH₄)₂^.PdCl₄
• Molecular Weight: 284.31
• CAS Registry Number: 13820-40-1
• EC Number: 237-498-6
• SMILES: [NH4+].[NH4+].Cl[Pd-2](Cl)(Cl)Cl

Properties

• Density: 2.17 g/mL (Expl.)

Safety Data

• Hazard Symbols: GHS07 Warning
• Hazard Statements: H302+H312+H332-H315-H319-H335
• Precautionary Statements: P261-P280-P305+P351+P338

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H302
Acute toxicity	Acute Tox.	4	H312
Eye irritation	Eye Irrit.	2	H319
Acute toxicity	Acute Tox.	4	H332
Specific target organ toxicity - single exposure	STOT SE	3	H335
Serious eye damage	Eye Dam.	1	H318
Substances or mixtures corrosive to metals	Met. Corr.	1	H290

• Transport Information: UN 3288

Discovory and Applicatios

Ammonium tetrachloropalladate is an inorganic coordination compound with the chemical formula (NH₄)₂\[PdCl₄]. It consists of two ammonium cations (NH₄⁺) paired with the tetrachloropalladate(II) anion \[PdCl₄]^2–, where palladium is in the +2 oxidation state coordinated to four chloride ions. This compound is a well-known palladium salt that appears as yellow to orange crystalline solids, commonly used as a palladium source in various chemical and industrial applications, particularly in catalysis and palladium complex synthesis.

The preparation of ammonium tetrachloropalladate generally involves dissolving palladium metal or palladium(II) chloride in hydrochloric acid followed by the addition of aqueous ammonium salts, such as ammonium chloride. This leads to the formation of the tetrachloropalladate(II) complex anion, which precipitates as the ammonium salt due to its limited solubility. The compound can be crystallized and purified through recrystallization from aqueous solutions.

Structurally, the \[PdCl₄]^2– anion adopts a square planar geometry typical for palladium(II) complexes, where the palladium ion is centrally coordinated to four chloride ligands arranged symmetrically. The ammonium cations act as counterions to balance the negative charge and are involved in hydrogen bonding within the crystal lattice. The compound’s crystalline structure is stabilized by ionic and hydrogen bonding interactions, contributing to its stability and characteristic properties.

Ammonium tetrachloropalladate is widely utilized as a precursor and catalyst in homogeneous and heterogeneous catalytic reactions. It serves as an easily handled and soluble source of palladium ions, which can be converted into active catalytic species under reaction conditions. Palladium-catalyzed cross-coupling reactions such as Suzuki-Miyaura, Heck, and Sonogashira couplings are prominent applications, enabling the formation of carbon–carbon and carbon–heteroatom bonds essential in pharmaceutical and materials chemistry.

Beyond catalysis, ammonium tetrachloropalladate is also used in electroplating and metal deposition processes. Its aqueous solutions allow for controlled palladium ion delivery, which is critical for plating thin, uniform palladium films on various substrates. These films are important in electronics, corrosion resistance, and catalysis.

The compound’s water solubility and stability under mildly acidic conditions make it a convenient starting material for the synthesis of various palladium complexes. By ligand substitution reactions, chloride ions in the complex can be replaced by phosphines, amines, or other ligands to generate tailored complexes for specialized catalytic applications.

Handling ammonium tetrachloropalladate requires care, as palladium compounds can be toxic if inhaled or ingested, and exposure may cause irritation. The compound is generally stable under ambient conditions but should be stored in a dry environment away from reducing agents and strong bases that could decompose the complex.

From an environmental perspective, waste containing palladium salts, including ammonium tetrachloropalladate, must be properly treated and recycled where possible due to the metal’s value and potential ecological impact. The recovery and reuse of palladium from spent catalysts and salts are important practices in sustainable chemistry.

Research continues to explore the reactivity and catalytic performance of palladium complexes derived from ammonium tetrachloropalladate. Modifications of ligands and reaction conditions aim to improve catalyst activity, selectivity, and durability in industrial and laboratory settings.

In summary, ammonium tetrachloropalladate is a palladium(II) complex salt composed of ammonium cations and the square planar tetrachloropalladate anion. It is commonly prepared by reaction of palladium sources with ammonium and chloride ions and is valued as a soluble palladium precursor in catalysis, electroplating, and complex synthesis. Its stability, solubility, and well-defined structure contribute to its widespread use, while appropriate safety and environmental handling ensure its responsible application in chemical and industrial fields.

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