- Nickel oxalate, typically encountered as nickel(II) oxalate dihydrate (NiC₂O₄·2H₂O), is an inorganic compound composed of divalent nickel ions (Ni²⁺) and oxalate anions (C₂O₄²⁻).
- It usually appears as a light green crystalline solid that is sparingly soluble in water and insoluble in most organic solvents. The compound belongs to the family of metal oxalates and is of interest in materials chemistry, coordination chemistry, and catalysis, particularly due to its clean thermal decomposition to nickel oxide or metallic nickel under specific conditions.
- Structurally, nickel(II) oxalate dihydrate consists of Ni²⁺ ions coordinated by bidentate oxalate ligands and water molecules, typically forming extended chains or layered networks. The oxalate ion, being a dicarboxylate, bridges nickel centers, contributing to a polymeric coordination structure. The dihydrate form is the most stable under ambient conditions, while the anhydrous form can be obtained by careful dehydration under vacuum or mild heating.
- Nickel oxalate can be synthesized by precipitation reactions between a soluble nickel salt, such as nickel sulfate or nickel chloride, and a soluble oxalate source like oxalic acid or sodium oxalate. The product precipitates out of aqueous solution as a fine green solid, which can be filtered, washed, and dried. Its synthesis is relatively straightforward and controllable, allowing for its use in both academic research and industrial settings.
- One of the most notable properties of nickel oxalate is its thermal decomposition behavior. Upon heating (usually above 300 °C), nickel oxalate breaks down to yield nickel oxide (NiO), along with carbon monoxide (CO) and carbon dioxide (CO₂) gases. When decomposed in a reducing atmosphere (e.g., in the presence of hydrogen), it can directly yield metallic nickel, making it a valuable precursor for producing high-purity nickel powders or nanostructures used in catalysts, batteries, and sintered materials. This thermal route is often used to obtain fine NiO particles for ceramic or electrochemical applications.
- Nickel oxalate has also been explored in coordination polymer and metal–organic framework (MOF) synthesis, where oxalate’s bridging ability and nickel’s versatile coordination behavior enable the construction of extended networks with tunable porosity and functionality.
- However, nickel oxalate is hazardous, primarily due to the toxicological properties of nickel and the potential for harmful gas release upon decomposition. It is classified as a carcinogen and skin sensitizer, and inhalation or ingestion should be strictly avoided. Furthermore, carbon monoxide released during thermal decomposition is a poisonous gas, requiring adequate ventilation and temperature control. For safe handling, personal protective equipment and adherence to environmental and workplace safety regulations are essential.
