Potassium octacyanomolybdate(IV) is the inorganic salt with the formula K₄ o(CN)₈ A yellow light-sensitive solid, it is the

potassium salt In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively ch ...

of the

cyanometalate Cyanometallates or cyanometalates are a class of coordination compounds, most often consisting only of cyanide ligands. Most are anions. Cyanide is a highly basic and small ligand, hence it readily saturates the coordination sphere of metal ions. ...

with the

coordination number In chemistry, crystallography, and materials science, the coordination number, also called ligancy, of a central atom in a molecule or crystal is the number of atoms, molecules or ions bonded to it. The ion/molecule/atom surrounding the central i ...

eight. The complex

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

consists of a Mo(IV) center bound to eight

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 ele ...

s resulting in an overall

charge Charge or charged may refer to: Arts, entertainment, and media Films * ''Charge, Zero Emissions/Maximum Speed'', a 2011 documentary Music * ''Charge'' (David Ford album) * ''Charge'' (Machel Montano album) * ''Charge!!'', an album by The Aqua ...

of −4, which is balanced with four potassium

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

. The salt is often prepared as its

dihydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was underst ...

K₄ o(CN)₈sup>.(H₂O)₂.

Preparation

The dihydrate K₄ o(CN)₈· 2 H₂O can be prepared by the reduction of

molybdate In chemistry a molybdate is a compound containing an oxoanion with molybdenum in its highest oxidation state of 6. Molybdenum can form a very large range of such oxoanions which can be discrete structures or polymeric extended structures, althou ...

(MoO₄^2-) with

potassium borohydride Borohydride refers to the anion , which is also called tetrahydroborate, and its salts. Borohydride or hydroborate is also the term used for compounds containing , where ''n'' is an integer from 0 to 3, for example cyanoborohydride or cyanotrihydr ...

(KBH₄) in a solution with

potassium cyanide Potassium cyanide is a compound with the formula KCN. This colorless crystalline salt, similar in appearance to sugar, is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications i ...

and

acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main componen ...

. Yields of 70% are typical and the method is suited for scale-up. :4MoO₄^2- + 32CN⁻ + BH₄⁻ + 25H⁺ → 4 o(CN)₈sup>4- + 13H₂O + H₃BO₃ An alternative route starts from MoCl₄(Et₂O)₂ avoiding the need for reductants. The yield of this route is typically around 70%. This synthesis is convenient for lower batch sizes than the earlier method but the MoCl₄(Et₂O)₂ is typically less available than the molybdate. :MoCl₄(Et₂O)₂ + 8KCN → K₄ o(CN)₈+ 4KCl + 2Et₂O

Reactions

Octacyanomolybdate(IV) can be oxidized to the

paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...

octacyanomolybdate(V). The cyanide ligands in o(CN)₈sup>4- remain basic. Strong acids lead to the

hydrogen isocyanide Hydrogen isocyanide is a chemical with the molecular formula HNC. It is a minor tautomer of hydrogen cyanide (HCN). Its importance in the field of astrochemistry is linked to its ubiquity in the interstellar medium. Nomenclature Both ''hydroge ...

complex o(CNH)₈sup>4+, in common with many

complexes.M. Sellin, V. Marvaud, M. Malischewski, "Isolation and Structural Characterization of Eightfold Protonated Octacyanometalates (CNH)₈sup>4+ (M=Mo^IV, W^IV) from Superacids", Angew. Chem. Int. Ed., 2020 volume 59, pp. 10519-10522. These ligands can be substituted by others, for example H₂O. The cyanide ligands also bind to other metals, leading to cages.

References

{{cyanides Cyano complexes Coordination complexes Molybdenum(IV) compounds Potassium compounds Cyanometallates