Zinc formate
[CAS 557-41-5]

Identification

• Classification: Organic raw materials >> Organometallic compound >> Organic zinc
• Name: Zinc formate
• Synonyms: zinc diformate
• Molecular Formula: C₂H₂ZnO₄
• Molecular Weight: 155.41
• CAS Registry Number: 557-41-5
• EC Number: 209-176-5
• SMILES: C(=O)[O-].C(=O)[O-].[Zn+2]

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H302-H319-H400-H410
• Safety Statements: P261-P271-P280

Discovery and Applications

Zinc formate is an inorganic–organic coordination compound consisting of zinc cations and formate anions derived from formic acid. It is one of the simplest metal carboxylates, where the formate ion (HCOO⁻) acts as a monodentate or bridging ligand to coordinate with Zn²⁺ centers, forming ionic or polymeric structures depending on the solid-state arrangement and hydration state.

Zinc, a d-block metal in group 12, commonly exhibits a +2 oxidation state with a filled d¹⁰ electronic configuration. Because of this electronic structure, zinc does not typically participate in redox chemistry under mild conditions but instead forms stable coordination compounds with oxygen-, nitrogen-, and sulfur-donor ligands. In zinc formate, the oxygen atoms of the formate ion serve as the primary coordination sites to the zinc center.

The formate ion is the simplest carboxylate anion, derived from formic acid. It contains a single carbonyl carbon bonded to a hydrogen atom, making it structurally distinct from larger carboxylates. In coordination chemistry, formate can bind to metal ions in several modes, including monodentate coordination through one oxygen atom, bidentate chelation through both oxygen atoms, or bridging coordination between multiple metal centers. In zinc formate, bridging coordination is common, leading to the formation of extended polymeric networks in the solid state.

The structural diversity of zinc formate arises from the flexible coordination geometry of Zn²⁺, which often adopts tetrahedral or octahedral coordination environments depending on ligand arrangement and hydration. In hydrated forms, water molecules can also coordinate to zinc, further modifying the crystal structure and hydrogen-bonding network.

From a physicochemical perspective, zinc formate is typically a white crystalline solid. It is generally soluble in water due to its ionic character, although solubility and crystallinity can vary depending on hydration and polymorphic form. In aqueous solution, it dissociates into Zn²⁺ ions and formate ions, where zinc may further exist as hydrated complexes.

Metal formates, including zinc formate, are part of a broader class of metal carboxylates that are widely studied in coordination chemistry, materials science, and catalysis. These compounds are of interest because they can serve as precursors for metal oxides through thermal decomposition. Upon heating, zinc formate can decompose to yield zinc oxide (ZnO), along with gaseous products such as carbon monoxide, carbon dioxide, and water.

Zinc oxide produced from such precursors is an important material used in catalysis, electronics, ceramics, and as a semiconductor. Therefore, zinc formate is often considered a convenient single-source precursor for ZnO synthesis under controlled thermal conditions.

In addition to materials applications, zinc compounds play important roles in biological systems. Zinc is an essential trace element involved in enzymatic catalysis, protein structure stabilization, and gene regulation. However, zinc formate itself is primarily of industrial and synthetic relevance rather than direct biological application.

The coordination behavior of zinc with carboxylates such as formate also serves as a model system in coordination chemistry for understanding metal–ligand interactions, polymeric structure formation, and solid-state organization. The relatively simple ligand structure allows detailed study of bonding motifs without excessive steric complexity.

Overall, zinc formate is a zinc(II) carboxylate coordination compound in which formate ions bind to Zn²⁺ centers through oxygen atoms to form ionic or polymeric structures. Its significance lies in coordination chemistry and materials applications, particularly as a precursor for zinc oxide and as a model system for studying metal–carboxylate interactions.