Copper(II) Formate (CAS 544-19-4)
Copper(II) Formate: Structure, Properties, and Applications
1. Introduction
Copper(II) formate (cupric formate) is the copper salt of formic acid. It typically exists as a dihydrate, Cu(HCOO)₂·2H₂O, and possesses interesting chemical and physical characteristics. Copper formate is used as a catalyst, a precursor for copper-based coatings, and in various research and industrial applications. This article reviews its chemical structure, physicochemical properties, synthesis methods, applications, and safety profile.
2. Chemical Structure and Nomenclature
Chemical formula: Cu(HCOO)₂ (anhydrous); Cu(HCOO)₂·2H₂O (dihydrate)
Molecular weight: 153.58 g/mol (anhydrous); 189.61 g/mol (dihydrate)
CAS number: 544-19-4 (anhydrous; often used for hydrates as well)
EC number: 208-865-8
Synonyms: Cupric formate, copper diformate, copper(II) methanoate
Structure: The copper center is in the +2 oxidation state, coordinated to formate anions. In the solid state, copper formate can form chain or layered structures where Cu²⁺ is coordinated by carboxylate groups.
3. Physicochemical Properties
Appearance: Blue-green crystalline powder (dihydrate). Anhydrous form is reported as blue powder.
Solubility: Soluble in water; insoluble in ethanol.
Stability: Stable under normal storage conditions. May decompose upon heating, releasing CO, CO₂, and metallic copper.
pH: Aqueous solutions are acidic.
Loss on drying: ~10.0%
4. Synthesis Methods
Reaction of copper hydroxide or carbonate with formic acid:
Cu(OH)₂ + 2 HCOOH → Cu(HCOO)₂ + 2 H₂O
or
CuCO₃ + 2 HCOOH → Cu(HCOO)₂ + CO₂ + H₂O
Ion exchange methods: Copper sulfate solutions can be passed through formate-loaded ion exchange resins.
Controlled crystallization: Used to obtain high-purity crystals.
5. Applications
Catalysis: Used as a catalyst or catalyst precursor in oxidation reactions, decarboxylation, and various organic transformations. In situ reduction can generate catalytically active copper nanoparticles.
Copper coating deposition: Thermal decomposition of copper formate on substrates produces thin copper films at relatively low temperatures, important for electronics, printed electronics, and MEMS applications.
Organic synthesis: Used in various synthetic routes requiring copper catalysis.
Research: Utilized in coordination chemistry studies, thermal decomposition investigations, and as a precursor for copper-based nanomaterials.
6. Safety and Toxicology
Toxicity: As a copper(II) compound, may cause skin, eye, and respiratory tract irritation. Copper ions can be toxic in excessive amounts. Formate ions may also contribute to toxicity, but risks are low when proper safety measures are followed.
Protective measures: Use gloves, safety goggles, and respiratory protection when handling powder. Ensure adequate ventilation.
Environmental aspects: Copper can be toxic to aquatic life at elevated concentrations. Formates are biodegradable, but copper compounds require proper disposal.
7. Conclusion
Copper(II) formate (CAS 544-19-4) is a versatile copper salt with applications in catalysis, low-temperature copper coating deposition, and organic synthesis. Its thermal decomposition to metallic copper makes it particularly valuable for printed electronics and thin-film technologies. While not as widely used as other copper salts, interest in copper formate is growing, especially in the development of eco-friendly deposition techniques and nanomaterial synthesis. Safety precautions should be observed due to the toxicity of copper compounds at elevated concentrations.