Zinc cyanide
Encyclopedia
Zinc cyanide is the inorganic compound
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...

 with the formula Zn
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

(C
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

N
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

)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
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

.

Structure, properties, synthesis

The structure features the zinc in the familiar tetrahedral coordination environment, all linked by bridging
Bridging ligand
A bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually restricted to small ligands such as pseudohalides or to ligands that are...

 cyanide
Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....

 ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...

s. The structure consists of two "interpenetrating" structures. Such motifs are sometimes called "expanded diamondoid
Diamondoid
A diamondoid, in the context of building materials for nanotechnology components, most generally refers to structures that resemble diamond in a broad sense: namely, strong, stiff structures containing dense, 3-D networks of covalent bonds, formed chiefly from first and second row atoms with a...

" structures because the interconnecting atoms are tetrahedral but instead of being directly linked as in diamond, the atoms are separated by additional bonds. Some forms of SiO2 adopts a similar structures, wherein the tetrahedral Si centres are linked by oxides. The cyanide group shows head to tail disorder with any zinc atom having between 1 and 4 carbon neighbours, and the remaining being nitrogen atoms. It shows one of the largest negative coefficents of thermal expansion (exceeding the previous record holder, zirconium tungstate).

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
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

, ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

, and additional cyanide to give anionic complexes.

Zn(CN)2 is fairly easy to make because combining aqueous solutions of cyanide and zinc ions. For commercial applications, some effort is made to avoid halide impurities by using zinc acetates. Zinc cyanide is a byproduct of certain gold extraction methods. To isolate gold from aqueous gold cyanide, some procedures call for the addition of zinc:
2 [Au(CN)2]- + Zn → 2 Au + Zn(CN)2 + 2 CN-

Applications

The main application of Zn(CN)2 is for electroplating of zinc from aqueous solutions containing additional cyanide.

Organic synthesis

Zn(CN)2 is employed as a catalyst for the cyanosilylation of aldehydes and ketones.

It is also used to introduce the formyl group in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...

. 2-Hydroxy-1-naphthaldehyde has been prepared from 2-naphthol, zinc cyanide, and anhydrous hydrogen chloride.
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