Copper(I) thiocyanate (or cuprous thiocyanate) is a

coordination polymer A coordination polymer is an inorganic or organometallic polymer structure containing metal cation centers linked by ligands. More formally a coordination polymer is a coordination compound with repeating coordination entities extending in 1, 2, o ...

with formula CuSCN. It is an air-stable, white solid used as a precursor for the preparation of other thiocyanate salts.

Structure

At least two polymorphs have been characterized by X-ray crystallography. They both feature copper(I) in a characteristic tetrahedral coordination geometry. The sulfur end of the SCN- ligand is triply bridging so that the coordination sphere for copper is CuS3N.Smith, D. L.; Saunders, V. I. "Preparation and Structure Refinement of the 2H Polytype of beta-Copper(I) Thiocyanate" Acta Crystallographica B, 1982, volume 38, 907-909.

Synthesis

Copper(I) thiocyanate forms from the spontaneous decomposition of black copper(II) thiocyanate, releasing

thiocyanogen Thiocyanogen, (SCN)2, is a pseudohalogen derived from the pseudohalide thiocyanate, CNsup>−. This hexatomic compound exhibits C2 point group symmetry and has the connectivity NCS-SCN. The oxidation ability is greater than bromine. It reacts w ...

, especially when heated. It is also formed from copper(II) thiocyanate under water, releasing (among others) thiocyanic acid and the highly poisonous

hydrogen cyanide Hydrogen cyanide, sometimes called prussic acid, is a chemical compound with the formula HCN and structure . It is a colorless, extremely poisonous, and flammable liquid that boils slightly above room temperature, at . HCN is produced on an ...

. It is conveniently prepared from relatively dilute solutions of copper(II) in water, such as copper(II) sulphate. To a copper(II) solution

sulphurous acid Sulfurous acid (also sulfuric(IV) acid, sulphurous acid (UK), sulphuric(IV) acid (UK)) is the chemical compound with the formula . There is no evidence that sulfurous acid exists in solution, but the molecule has been detected in the gas phase. ...

is added and then a soluble thiocyanate is added (preferably slowly, while stirring). Copper(I) thiocyanate is precipitated as a white powder. Alternatively, a thiosulfate solution may be used as a reducing agent.

Double salts

Copper(I) thiocyanate forms one double salt with the group 1 elements, CsCu(SCN)₂. The double salt only forms from concentrated solutions of CsSCN, into which CuSCN dissolves. From less concentrated solutions, solid CuSCN separates reflecting its low solubility. When brought together with potassium, sodium or

barium thiocyanate Barium thiocyanate is a colorless water-soluble salt that is very hygroscopic. It is highly toxic to ingestion and irritates the skin. It is also soluble in most alcohols and insoluble in simple alkanes. Uses Barium thiocyanate is used in dyeing ...

, and brought to crystallisation by concentrating the solution, mixed salts will crystallise out. These are not considered true double salts. As with CsCu (SNC)₂, copper(I) thiocyanate separates out when these mixed salts are redissolved or their solutions diluted.

Uses

Copper(I) thiocyanate is a hole conductor, a semiconductor with a wide band gap (3.6 eV, therefore transparent to visible and near infrared light). It is used in photovoltaics in some third-generation cells as a hole transfer layer. It acts as a

P-type semiconductor An extrinsic semiconductor is one that has been '' doped''; during manufacture of the semiconductor crystal a trace element or chemical called a doping agent has been incorporated chemically into the crystal, for the purpose of giving it different ...

and as a solid-state electrolyte. It is often used in

dye-sensitized solar cell A dye-sensitized solar cell (DSSC, DSC, DYSC or Grätzel cell) is a low-cost solar cell belonging to the group of thin film solar cells. It is based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a '' photoelectr ...

s. Its hole conductivity is however relatively poor (0.01 S·m⁻¹). This can be improved by various treatments, e.g. exposure to gaseous chlorine or doping with (SCN)₂. CuSCN with NiO act synergically as a smoke suppressant additive in polyvinyl chloride (PVC). CuSCN precipitated on carbon support can be used for conversion of aryl halides to aryl thiocyanates. Copper thiocyanate is used in some anti-fouling paints.V.F. Vetere et al, "Solubility and Toxic Effect of the Cuprous Thiocyanate Antifouling Pigment on Barnacle Larvae", Journal of Coatings Technology, 69:39 (March 1997)
/ref> Advantages compared to cuprous oxide include that the compound is white and a more efficient

biocide A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. The US Environmental Protection Agency (EPA) uses a slig ...

References

{{DEFAULTSORT:Copper(I) thiocyanate Copper(I) compounds Thiocyanates Semiconductor materials Coordination polymers