Hofmann clathrates

In inorganic chemistry, Hofmann clathrates refers to materials with the formula Ni(CN)2(NH3)(C6H6). These materials are a type of coordination polymer.[1] 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).[2]

## Structures

Structure of Ni(CN)2(NH3)(C6H6). Some N-H bonds are omitted.[3]

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.

## 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.

## References

1. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1161. ISBN 978-0-08-037941-8.
2. ↑ O. M. Yaghi; M. J. Kalmutzki; C. S. Diercks (2019). Introduction to Reticular Chemistry: Metal-Organic Frameworks and Covalent Organic Frameworks. Weinheim: Wiley-VCH.
3. ↑ Büttner, H. G.; Kearley, G. J.; Howard, C. J.; Fillaux, F. (1994). "Structure of the Hofmann Clathrates Ni(NH3)2Ni(CN)4.2C6D6 and Zn(NH3)2Ni(CN)4.2C6H6". Acta Crystallographica Section B: Structural Science 50 (4): 431–435. doi:10.1107/S0108768193013539.

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