ZINC OXALATE

Zinc oxalate (ZnC₂O₄, CAS No. 547-68-2), also known as zinc ethanedioate, is a metal-organic coordination compound with significant applications in materials science, catalysis, and pharmaceuticals. 
This comprehensive review explores various synthesis methods, structural characteristics, physicochemical properties, and diverse applications of zinc oxalate. 
Special emphasis is placed on its role as a precursor for zinc oxide nanoparticles, its catalytic properties, and its emerging biomedical uses. 
The thermal decomposition behavior, coordination chemistry, and environmental impact of zinc oxalate are also discussed in detail.
CAS No. 547-68-2
Zinc oxalate, ZnC₂O₄, zinc ethanedioate, metal-organic frameworks, thermal decomposition, nanomaterials, catalysis, biomedical applications.

Zinc oxalate (ZnC₂O₄, CAS No. 547-68-2), also referred to as zinc ethanedioate or zinc(II) oxalate, is a coordination compound formed by the reaction of zinc ions (Zn²⁺) with oxalic acid (H₂C₂O₄). 
It is a member of the metal oxalate family, which includes compounds such as iron oxalate (FeC₂O₄) and copper oxalate (CuC₂O₄). 
Zinc oxalate is of particular interest due to its ability to decompose into zinc oxide (ZnO) under controlled thermal conditions, making it a valuable precursor for the synthesis of ZnO nanoparticles, which have wide-ranging applications in electronics, photonics, and biomedicine.

The compound exhibits a layered structure with zinc ions coordinated by oxalate ligands, forming a porous framework that can be exploited for gas storage and catalysis. 
Additionally, its low solubility in water and stability under ambient conditions make it suitable for various industrial and environmental applications.

This review provides an in-depth analysis of the synthesis, structural properties, and applications of zinc oxalate, with a focus on recent advancements and future prospects in the field.

Synthesis of Zinc Oxalate
Precipitation Method
The precipitation method is the most straightforward and widely used technique for synthesizing zinc oxalate. 
It involves the reaction of a soluble zinc salt (e.g., zinc sulfate, ZnSO₄, or zinc chloride, ZnCl₂) with oxalic acid (H₂C₂O₄) in an aqueous medium. 
The chemical reaction can be represented as:
The white precipitate of zinc oxalate is filtered, washed with distilled water to remove impurities, and dried at 60–80°C. 
The particle size and morphology can be controlled by adjusting parameters such as pH, temperature, and reactant concentration.

Advantages:
Simple and cost-effective
High yield and purity
Disadvantages:
Limited control over particle size distribution
Potential for impurity incorporation

Hydrothermal Synthesis
Hydrothermal synthesis involves the reaction of zinc precursors with oxalic acid in a sealed autoclave at elevated temperatures (120–200°C) and pressures. 
This method allows for the growth of well-defined crystals with controlled morphology.

Procedure:
Dissolve zinc nitrate (Zn(NO₃)₂) and oxalic acid in deionized water.
Transfer the solution to a Teflon-lined autoclave.
Heat at 150°C for 12–24 hours.
Cool naturally, collect the precipitate, and dry.
Advantages:
High crystallinity
Tunable morphology (nanorods, microplates)
Disadvantages:
Energy-intensive
Requires specialized equipment

Sol-Gel Method
The sol-gel method involves the formation of a colloidal suspension (sol) that transitions into a gel, which is then calcined to produce zinc oxalate.

Steps:
Mix zinc acetate (Zn(CH₃COO)₂) with oxalic acid in ethanol.
Stir to form a homogeneous sol.
Age the sol to form a gel.
Dry and calcine at 200–300°C.
Advantages:
High purity
Uniform particle size
Disadvantages:
Long processing time
Shrinkage during drying

Mechanochemical Synthesis
Mechanochemical synthesis is a solvent-free method where zinc oxide (ZnO) and oxalic acid are ground in a ball mill. 
The mechanical energy induces a solid-state reaction:

Advantages:
Eco-friendly (no solvents)
Scalable
Disadvantages:
Broad particle size distribution
Contamination from milling media

Electrochemical Synthesis
Electrochemical synthesis involves the anodic dissolution of zinc metal in an oxalate-containing electrolyte.
Procedure:

Use a zinc anode and inert cathode in Na₂C₂O₄ solution.
Apply a constant current (10–50 mA/cm²).
Collect the deposited zinc oxalate.
Advantages:
High purity
Controlled film thickness
Disadvantages:
Limited to thin films
Requires precise control

Biological and Green Synthesis Approaches
Recent studies have explored the use of plant extracts or microbial cultures to synthesize zinc oxalate under mild conditions.
Example:
Fungal-mediated synthesis using Aspergillus niger.
Advantages:
Environmentally benign
Low energy consumption
Disadvantages:
Low yield
Long reaction time

Crystal Structure and Characterization
X-ray Diffraction (XRD) Analysis
Zinc oxalate typically crystallizes in a monoclinic system (space group *P2₁/c*) with lattice parameters *a* = 5.98 Å, *b* = 5.42 Å, *c* = 9.82 Å, and β = 114.5°. XRD patterns show characteristic peaks at 2θ = 18.5°, 24.3°, and 30.1°.

Infrared (IR) and Raman Spectroscopy
IR peaks:
1620 cm⁻¹ (C=O stretch)
1320 cm⁻¹ (C-O stretch)
500 cm⁻¹ (Zn-O vibration)
Raman bands:
1460 cm⁻¹ (oxalate symmetric stretch)

Thermal Analysis (TGA/DSC)
TGA: Weight loss in two stages:
Dehydration (50–150°C)
Decomposition to ZnO (300–400°C)
DSC: Endothermic peak at 350°C (oxalate decomposition).

Morphological Studies (SEM/TEM/AFM)
SEM: Reveals plate-like or rod-like structures.
TEM: Confirms nanocrystalline nature.
AFM: Measures surface roughness.

Nuclear Magnetic Resonance (NMR) Spectroscopy
¹³C NMR shows a peak at 160 ppm (carbonyl carbon).

X-ray Photoelectron Spectroscopy (XPS)
Zn 2p₃/₂ peak at 1021.5 eV.
O 1s peak at 531.2 eV.

Physicochemical Properties
Solubility and Stability
Solubility: 0.004 g/100 mL (water, 25°C).
Stability: Stable in air but decomposes in acids.

Optical Properties
Bandgap: ~3.8 eV (UV-active).

Magnetic Properties
Diamagnetic (no unpaired electrons).

Electrical Conductivity
Insulating (σ ~ 10⁻¹⁰ S/cm).

Applications of Zinc Oxalate
Precursor for Zinc Oxide Nanoparticles
Calcination at 400°C yields pure ZnO for sensors and LEDs.

Catalysis and Chemical Reactions
Used in esterification and oxidation reactions.

Biomedical Applications
Antibacterial coatings for implants.

Environmental Remediation
Adsorbent for heavy metals (Pb²⁺, Cd²⁺).

Energy Storage and Conversion
Anode material for Li-ion batteries.

SAFETY INFORMATION ABOUT ZINC OXALATE

First aid measures:
Description of first aid measures:
General advice:
Consult a physician. 
Show this safety data sheet to the doctor in attendance.
Move out of dangerous area:
 
If inhaled:
If breathed in, move person into fresh air. 
If not breathing, give artificial respiration.
Consult a physician.
In case of skin contact:
Take off conSAFETYtaminated clothing and shoes immediately. 
Wash off with soap and plenty of water.
Consult a physician.
 
In case of eye contact:
Rinse thoroughly with plenty of water for at least 15 minutes and consult a physician.
Continue rinsing eyes during transport to hospital.
 
If swallowed:
Do NOT induce vomiting. 
Never give anything by mouth to an unconscious person. 
Rinse mouth with water. 
Consult a physician.
 
Firefighting measures:
Extinguishing media:
Suitable extinguishing media:
Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide.
Special hazards arising from the substance or mixture
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas
 
Advice for firefighters:
Wear self-contained breathing apparatus for firefighting if necessary.
Accidental release measures:
Personal precautions, protective equipment and emergency procedures
Use personal protective equipment. 
 
Avoid breathing vapours, mist or gas. 
Evacuate personnel to safe areas.
 
Environmental precautions:
Prevent further leakage or spillage if safe to do so.
Do not let product enter drains.
Discharge into the environment must be avoided.
 
Methods and materials for containment and cleaning up:
Soak up with inert absorbent material and dispose of as hazardous waste. 
Keep in suitable, closed containers for disposal.
 
Handling and storage:
Precautions for safe handling:
Avoid inhalation of vapour or mist.
 
Conditions for safe storage, including any incompatibilities:
Keep container tightly closed in a dry and well-ventilated place. 
Containers which are opened must be carefully resealed and kept upright to prevent leakage.
Storage class (TRGS 510): 8A: Combustible, corrosive hazardous materials
 
Exposure controls/personal protection:
Control parameters:
Components with workplace control parameters
Contains no substances with occupational exposure limit values.
Exposure controls:
Appropriate engineering controls:
Handle in accordance with good industrial hygiene and safety practice.
Wash hands before breaks and at the end of workday.
 
Personal protective equipment:
Eye/face protection:
Tightly fitting safety goggles. 
Faceshield (8-inch minimum). 
Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU).
 
Skin protection:
Handle with gloves. 
Gloves must be inspected prior to use. 
Use proper glove
removal technique (without touching glove's outer surface) to avoid skin contact with this product. 
Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices. 
Wash and dry hands.
 
Full contact:
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
Splash contact
Material: Nitrile rubber
Minimum layer thickness: 0.11 mm
Break through time: 480 min
Material tested:Dermatril (KCL 740 / Aldrich Z677272, Size M)
It should not be construed as offering an approval for any specific use scenario.
 
Body Protection:
Complete suit protecting against chemicals, The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace.
Respiratory protection:
Where risk assessment shows air-purifying respirators are appropriate use a fullface respirator with multi-purpose combination (US) or type ABEK (EN 14387) respirator cartridges as a backup to engineering controls. 
 
If the respirator is the sole means of protection, use a full-face supplied air respirator. 
Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU).
Control of environmental exposure
Prevent further leakage or spillage if safe to do so. 
Do not let product enter drains.
Discharge into the environment must be avoided.
 
Stability and reactivity:
Chemical stability:
Stable under recommended storage conditions.
Incompatible materials:
Strong oxidizing agents:
Hazardous decomposition products:
Hazardous decomposition products formed under fire conditions. 
Carbon oxides, Nitrogen oxides (NOx), Hydrogen chloride gas.
 
Disposal considerations:
Waste treatment methods:
Product:
Offer surplus and non-recyclable solutions to a licensed disposal company. 
Contact a licensed professional waste disposal service to dispose of this material.
Contaminated packaging:
Dispose of as unused product