A complex cyanide is a coordination compound where one or more cyanide (CN⁻) groups are coordinated to a central metal atom, forming a stable complex ion — for example, the hexacyanoferrate anion in potassium ferricyanide. Simple cyanide salts (like sodium or potassium cyanide) are ionic compounds with a free cyanide anion. This chemical distinction determines whether a product classifies under heading 2837 (simple cyanides) or 2837 subheading 20 (complex cyanides), and misclassification is a common audit finding.

Complex cyanides generally have significantly lower acute toxicity than free cyanide salts because the cyanide is tightly bound within the coordination complex. However, EPA TSCA certification is still required at import, and SDS documentation must accompany the shipment. The specific regulatory burden varies by compound — importers should confirm requirements with a licensed customs broker and review the relevant EPA chemical listings before entry.