Rhodium (III) chloride trihydrate
[CAS# 20765-98-4]

Identification

• Classification: Inorganic chemical industry >> Inorganic salt >> Metal halides and halides >> Metal chlorides and salts
• Name: Rhodium (III) chloride trihydrate
• Molecular Formula: RhCl₃.3(H₂O)
• Molecular Weight: 263.31
• CAS Registry Number: 20765-98-4
• EC Number: 606-630-8
• SMILES: Cl[Rh](Cl)Cl.O.O.O

Properties

• Melting point: 100 °C (dec.)
• Water solubility: soluble

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H302
• Safety Statements: P264-P270-P301+P312+P330-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Serious eye damage	Eye Dam.	1	H318
Substances or mixtures corrosive to metals	Met. Corr.	1	H290
Germ cell mutagenicity	Muta.	2	H341
Chronic hazardous to the aquatic environment	Aquatic Chronic	1	H410
Acute hazardous to the aquatic environment	Aquatic Acute	1	H400
Skin sensitization	Skin Sens.	1	H317
Skin corrosion	Skin Corr.	1C	H314
Skin irritation	Skin Irrit.	2	H315
Acute toxicity	Acute Tox.	4	H312
Acute toxicity	Acute Tox.	4	H332

Discovery and Applications

Rhodium(III) chloride trihydrate, commonly represented by the formula RhCl₃·3H₂O, is an inorganic coordination compound composed of rhodium in the +3 oxidation state complexed with chloride ions and water molecules. It typically appears as a dark red to brown crystalline solid and is soluble in water and some polar solvents.

This compound is generally prepared by dissolving rhodium metal or rhodium-containing alloys in hydrochloric acid, followed by controlled crystallization to obtain the trihydrate form. The trihydrate contains three molecules of crystallization water per formula unit, which are coordinated or hydrogen-bonded in the crystal lattice.

Structurally, rhodium(III) chloride trihydrate contains octahedrally coordinated rhodium centers, typically bound to chloride ligands and water molecules. The coordination environment may vary depending on hydration and crystallization conditions, but the rhodium ion commonly adopts an octahedral geometry characteristic of d⁶ metal ions in the +3 oxidation state.

Rhodium(III) chloride trihydrate is widely used as a precursor in the synthesis of rhodium-based catalysts and organometallic complexes. It serves as a starting material for preparing homogeneous catalysts applied in hydrogenation, hydroformylation, and other important industrial catalytic reactions. The compound’s reactivity allows ligand substitution to form diverse rhodium complexes with phosphines, amines, and other ligands tailored for specific catalytic functions.

In materials science, rhodium(III) chloride trihydrate is employed in the fabrication of rhodium films and nanoparticles via chemical or electrochemical deposition. These materials are used in electronics, catalytic converters, and fuel cells due to rhodium’s excellent catalytic activity and corrosion resistance.

From an analytical perspective, the compound is used in laboratories for rhodium quantification and as a standard reagent in various chemical syntheses involving rhodium. It is often chosen for its relatively high stability and ease of handling compared to other rhodium salts.

Handling rhodium(III) chloride trihydrate requires appropriate safety precautions as it is an irritant and may pose risks upon inhalation or skin contact. Standard laboratory practices including the use of gloves, eye protection, and working in a fume hood are recommended.

Upon heating, rhodium(III) chloride trihydrate loses its water of crystallization and eventually decomposes to rhodium(III) oxide or metallic rhodium under reducing conditions. These thermal properties are exploited in catalyst preparation and material synthesis.

In summary, rhodium(III) chloride trihydrate is a water-containing rhodium(III) coordination compound widely utilized as a catalyst precursor, reagent in organometallic synthesis, and in material fabrication. Its octahedral coordination geometry and aqueous solubility make it a versatile and important compound in rhodium chemistry and industrial applications.

References

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