- Cadmium cyanide is an inorganic coordination compound with the formula Cd(CN)₂, composed of divalent cadmium cations (Cd²⁺) coordinated to cyanide anions (CN⁻). The cyanide ion consists of a carbon atom triple-bonded to a nitrogen atom, carrying a net −1 charge.
- The compound has a molar mass of 164.44 g/mol and is usually encountered as a white crystalline solid. It is odorless in pure form, but if hydrolyzed or decomposed, it releases highly toxic hydrogen cyanide (HCN) gas, which has a faint bitter-almond smell detectable by some individuals.
- Cadmium cyanide typically crystallizes in a cubic lattice similar to zinc cyanide, forming a three-dimensional coordination polymer in which cadmium atoms are linked by cyanide bridges. It is only sparingly soluble in water but dissolves readily in excess aqueous cyanide due to the formation of soluble complex ions such as [Cd(CN)₄]²⁻. It is insoluble in most organic solvents. Its density is about 2.32 g/cm³, and it decomposes before melting.
- Cadmium cyanide can be synthesized by several methods, the most common being:
- Reaction of cadmium salts with potassium or sodium cyanide: Cd(NO₃)₂ + 2 KCN → Cd(CN)₂↓ + 2 KNO₃
- Absorption of hydrogen cyanide into cadmium hydroxide or oxide slurries: CdO + 2 HCN → Cd(CN)₂ + H₂O
- The resulting precipitate is washed thoroughly to remove excess cyanide and dried under controlled conditions to avoid hydrolysis.
- Cadmium cyanide is stable in neutral, dry conditions, but in acidic environments it reacts rapidly to release hydrogen cyanide gas: Cd(CN)₂ + 2 H⁺ → Cd²⁺ + 2 HCN↑
- It can form complex cyanide salts such as potassium tetracyanocadmate K₂[Cd(CN)₄], which are more soluble in water. When strongly heated, cadmium cyanide decomposes into cadmium metal and cyanogen gas or cadmium cyanide vapor, which can further decompose to carbon and nitrogen species.
- The primary use of cadmium cyanide has been in electroplating baths for depositing thin, corrosion-resistant layers of cadmium onto steel, copper, and other metals. In plating baths, it is usually present as part of a complex cyanide solution containing sodium cyanide or potassium cyanide to improve conductivity and control deposition quality. Cadmium coatings are valued for their corrosion resistance, lubricity, and solderability, especially in aerospace and military hardware. However, due to its extreme toxicity, cadmium cyanide use has sharply declined in favor of less hazardous alternatives such as zinc-nickel plating.
- Cadmium cyanide is extremely toxic due to the combined effects of cadmium and cyanide ions. Cyanide interferes with cellular respiration by binding to cytochrome oxidase in mitochondria, causing rapid onset of hypoxia at the cellular level. Acute cyanide poisoning can cause dizziness, weakness, nausea, rapid breathing, seizures, loss of consciousness, and death within minutes at high exposure levels. Cadmium toxicity contributes to long-term organ damage, particularly to the kidneys and bones, and is carcinogenic with chronic exposure. Even very small quantities can be lethal if ingested, inhaled, or absorbed through damaged skin.
- Cadmium cyanide is highly toxic to aquatic life and persistent in the environment. Accidental releases can cause immediate fish kills and long-term contamination of waterways. Cyanide can degrade in the environment under sunlight and certain chemical conditions, but cadmium remains as a persistent heavy metal contaminant. Due to these risks, its production, use, and disposal are strictly regulated worldwide.
- Cadmium cyanide is classified as a highly toxic material under chemical safety regulations, with combined hazard classifications for both cyanides and cadmium compounds. It generally falls under UN 1575 – Cadmium cyanide, hazard class 6.1 (toxic substances), packing group I (highest danger). Occupational exposure limits are extremely low—often ≤0.005 mg/m³ (as Cd) and ≤5 mg/m³ (as CN⁻, short-term)—and work with it must be done in closed systems or fume hoods, with full PPE and cyanide antidote kits available.
