Zinc cyanide


Zinc cyanide is the inorganic compound with the formula Zn2. It is a white solid that is used mainly for electroplating zinc but also has more specialized applications for the synthesis of organic compounds.

Structure

In Zn2, zinc adopts the tetrahedral coordination environment, all linked by bridging cyanide ligands. The structure consists of two "interpenetrating" structures. Such motifs are sometimes called "expanded diamondoid" structures. Some forms of SiO2 adopt a similar structure, wherein the tetrahedral Si centres are linked by oxides. The cyanide group shows head to tail disorder with any zinc atom having between one and four carbon neighbours, and the remaining being nitrogen atoms. It shows one of the largest negative coefficients of thermal expansion.

Chemical properties

Typical for an inorganic polymer, Zn2 is insoluble in most solvents. The solid dissolves in, or more precisely, is degraded by, aqueous solutions of basic ligands such as hydroxide, ammonia, and additional cyanide to give anionic complexes.

Synthesis

Zn2 is fairly easy to make by combining aqueous solutions of cyanide and zinc ions, for example via the double replacement reaction between KCN and ZnSO4:
For commercial applications, some effort is made to avoid halide impurities by using acetate salts of zinc:
Zinc cyanide is also produced as a byproduct of certain gold extraction methods. Procedures to isolate gold from aqueous gold cyanide sometimes call for the addition of zinc:

Applications

Electroplating

The main application of Zn2 is for electroplating of zinc from aqueous solutions containing additional cyanide.

Organic synthesis

Zn2 is used to introduce the formyl group in to aromatic compounds in the Gatterman reaction where it serves a convenient, safer, and non-gaseous alternative to HCN. Because the reaction uses HCl, Zn2 also supplies the reaction with ZnCl2 in-situ, a Lewis acid catalyst. Examples of Zn2 being used in this way include the synthesis of 2-Hydroxy-1-nafthaldehyde and Mesitaldehyde.
Zn2 is also employed as a catalyst for the cyanosilylation of aldehydes and ketones.