inorganic chemistry Inorganic chemistry deals with synthesis and behavior of inorganic and organometallic compounds. This field covers chemical compounds that are not carbon-based, which are the subjects of organic chemistry. The distinction between the two disci ...

, Hofmann clathrates refers to materials with the formula Ni(CN)₂(NH₃)(C₆H₆). These materials are a type of

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 ...

. They have attracted attention because they can be used to separate

xylene In organic chemistry, xylene or xylol (; IUPAC name: dimethylbenzene) are any of three organic compounds with the formula . They are derived from the substitution of two hydrogen atoms with methyl groups in a benzene ring; which hydrogens are sub ...

s. On a conceptual level, Hofmann clathrates can be viewed as forerunners to metal-organic frameworks (MOFs).

Structures

The empirical formula Ni(CN)₂(NH₃)(C₆H₆) reflects the presence of two types of nickel(II) centers, one of which is the square-planar

tetracyanonickelate The cyanonickelates are a class of chemical compound containing anions consisting of nickel atoms, and cyanide groups. The most important of these are the tetracyanonickelates containing four cyanide groups per nickel. The tetracyanonickelates c ...

, i(CN)₄sup>2-. The second kind of nickel site consists of i(NH₃)₂sup>2+ groups that are connected to the Ni-CN nitrogens. Thus cyanide serves as a

bridging ligand In coordination chemistry, 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 r ...

. The linking of the i(CN)₄sup>2- and ''trans''- i(NH₃)₂sup>2+ subunits results in a sheet-like polymer. Voids between these sheets, defined by the ammonia ligands, are occupied by benzene molecules.

Variations

Many variations of Hofmann clathrates have been reported. The ammonia ligands can be replaced by

diamine A diamine is an amine with exactly two amino groups. Diamines are used as monomers to prepare polyamides, polyimides, and polyureas. The term ''diamine'' refers mostly to primary diamines, as those are the most reactive. In terms of quantities p ...

s. Tetracyanonickelate can be replaced by tetracyanopalladate. A wide range of

arene 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 grouping ...

s can occupy the benzene site.

References

Nickel complexes Cyano complexes Cyanometallates