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Hofmann clathrates

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In inorganic chemistry, Hofmann clathrates refers to materials with the formula Ni(CN)2(NH3)(C6H6). These materials are a type of coordination polymer that have properties of inclusion compounds.[1][2] They have attracted attention because they can be used to separate xylenes. On a conceptual level, Hofmann clathrates can be viewed as forerunners to metal–organic frameworks (MOFs).[3]

Structures

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Structure of Ni(CN)2(NH3)(C6H6). Some N-H bonds are omitted.[4]

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, [Ni(CN)4]2-. The second kind of nickel site consists of [Ni(NH3)2]2+ groups that are connected to the Ni-CN nitrogens. Thus cyanide serves as a bridging ligand. The linking of the [Ni(CN)4]2- and trans-[Ni(NH3)2]2+ subunits results in a sheet-like polymer. Voids between these sheets, defined by the ammonia ligands, are occupied by benzene molecules.

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Variations

Many variations of Hofmann clathrates have been reported. The ammonia ligands can be replaced by diamines. Tetracyanonickelate can be replaced by tetracyanopalladate. A wide range of arenes can occupy the benzene site.

See also

References

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