Magnesium cyanide

Magnesium cyanide is a chemical compound with the formula Mg(CN)₂. It is a toxic white solid. Unlike calcium isocyanide, the cyanide ligands prefer to coordinate at carbon, with a 0.3‑kcal/mol isomerization barrier.^[1] When this salt is heated to 500 °C, it decomposes to magnesium nitride.^[2]

Magnesium cyanide

Names
Other names Magnesium dicyanide Magnesium(II) cyanide
Identifiers
3D model (JSmol)	Interactive image
PubChem CID	14205320
InChI InChI=1S/2CN.Mg/c2*1-2;/q2*-1;+2 Key: FKWSMBAMOQCVPV-UHFFFAOYSA-N
SMILES [C-]#N.[C-]#N.[Mg+2]
Properties
Chemical formula	Mg(CN)2
Molar mass	76.34 g/mol
Appearance	White solid
Melting point	500 °C (932 °F; 773 K) (decomposes)
Solubility in water	Reacts to form magnesium hydroxide
Solubility in ammonia	Slightly soluble
Related compounds
Other anions	Magnesium thiocyanate
Other cations	Calcium cyanide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Preparation

The first attempt to prepare magnesium cyanide was attempted in 1924. It was attempted by reacting a solution of hydrogen cyanide in water with magnesium metal:^[2]

HCN + Mg → Mg(CN)₂ + H₂

However, no magnesium cyanide was observed, only magnesium hydroxide formed. To avoid this problem, instead of using water as the reaction medium, pure ammonia was used at -30 °C. This formed magnesium cyanide ammoniate, which in turn was heated to 180 °C to produce magnesium cyanide.^[3] Other methods are possible, such as the decomposition of magnesium ferricyanide in an electric carbon tube, which produces iron carbide as a byproduct.^[2]

Complexes

Magnesium cyanide reacts with silver nitrate to form magnesium silver cyanide, with the formula MgAg₂(CN)₄. When this compound is heated it produces hydrogen cyanide gas and magnesium hydroxide in the presence of water, which meant it could not be used as a pathway for the production of magnesium cyanide. When silver nitrate reacts with magnesium cyanide, it also produces another magnesium silver cyanide, with the formula MgAg(CN)₃.^[2]

Toxicity

Main article: Cyanide poisoning

Magnesium cyanide, like all cyanides, is extremely toxic. When it enters the body, it inhibits tissue respiration enzymes, and tissues lose the ability to absorb oxygen from the blood.^[4]