Zinc cyanide is the
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemis ...
with the formula
Zn(
CN)
2. 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 Zn(CN)
2, zinc adopts the tetrahedral coordination environment, all linked by
bridging cyanide
Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms.
In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...
ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elect ...
s. The structure consists of two "interpenetrating" structures (blue and red in the picture above). Such motifs are sometimes called "expanded
diamondoid" structures. Some forms of SiO
2 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 (exceeding the previous record holder,
zirconium tungstate
Zirconium tungstate () is the zirconium salt of tungstic acid and has unusual properties. The phase formed at ambient pressure by reaction of ZrO2 and WO3 is a metastable cubic phase, which has ''negative thermal expansion'' characteristics, n ...
).
Chemical properties
Typical for an inorganic polymer, Zn(CN)
2 is insoluble in most solvents. The solid dissolves in, or more precisely, is degraded by, aqueous solutions of basic ligands such as
hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. ...
,
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
, and additional cyanide to give anionic complexes.
Synthesis
Zn(CN)
2 is easy to make by combining aqueous solutions of cyanide and zinc ions, for example via the
double replacement reaction
A salt metathesis reaction, sometimes called a double displacement reaction, is a chemical process involving the exchange of bonds between two reacting chemical species which results in the creation of products with similar or identical bonding ...
between
KCN and
ZnSO4:
: ZnSO
4 + 2 KCN → Zn(CN)
2 +
K2SO4
For commercial applications, some effort is made to avoid
halide
In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a flu ...
impurities by using
acetate
An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called ...
salts of zinc:
[
: Zn(CH3COO)2 + HCN → Zn(CN)2 + 2 CH3COOH
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:
: 2 u(CN)2sup>− + Zn → 2 Au + Zn(CN)2 + 2 CN−
]
Applications
Electroplating
The main application of Zn(CN)2 is for electroplating of zinc from aqueous solutions containing additional cyanide.[Ernst Gail, Stephen Gos, Rupprecht Kulzer, Jürgen Lorösch, Andreas Rubo and Manfred Sauer "Cyano Compounds, Inorganic" Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2004. ]
Organic synthesis
Zn(CN)2 is used to introduce the formyl group in to aromatic compounds
Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past groupin ...
in the Gatterman reaction where it serves a convenient, safer, and non-gaseous alternative to HCN. Because the reaction uses HCl HCL may refer to:
Science and medicine
* Hairy cell leukemia, an uncommon and slowly progressing B cell leukemia
* Harvard Cyclotron Laboratory, from 1961 to 2002, a proton accelerator used for research and development
* Hollow-cathode lamp, a s ...
, Zn(CN)2 also supplies the reaction ''in situ'' with ZnCl2, a Lewis acid catalyst. Examples of Zn(CN)2 being used in this way include the synthesis of 2-hydroxy-1-naphthaldehyde and mesitaldehyde.
Zn(CN)2 is also employed as a catalyst for the cyanosilylation of aldehydes and ketones.
References
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
cyanide
Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms.
In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...
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