The synthesis of the first carbon-free inorganic sandwich compound [Os(η5-B5H10)2] (which is an osmium ion sandwiched between two boron rings) is a fundamental advancement in chemistry because it expands the concept beyond organometallic to inorganometallic. This was sought by chemists for seven decades since discovery of Ferrocene Fe(C5H5)2 in 1951. Ferrocene has a symmetrical sandwich structure where a central iron atom placed between two flat C5H5 rings is bound (by the two carbon rings) through delocalised π electrons.
Ferrocene Fe(C5H5)2 is an important organometallic compound. It was discovered in 1951. It has a symmetrical sandwich structure where a central iron atom between two planar C5H rings is bound (by the two carbon rings) through delocalised π electrons resulting in a stable 18-electron configuration.
Unravelling of this molecular structure based on a new way of chemical bonding between metals and flat organic rings through delocalised π-electrons above and below the rings yielding stable sandwich compounds was a milestone in chemistry. It contributed to the understanding of chemical interaction metals with organic molecules and led to beginning of a new field of organometallic chemistry. Many such sandwich compounds have been developed since discovery of Ferrocene that have found wide ranging industrial applications as catalysts and in electrochemical sector.
Chemists wondered whether inorganic non-carbon rings would give rise to a stable sandwich compound like Ferrocene. For the last even decades, researchers attempted to synthesise stable Ferrocene analog with inorganic rings. On 23 April 2026, scientists reported successful synthesis of a carbon-free sandwich compound that is stable.
The new carbon-free sandwich compound is [Os(η5-B5H10)2] which is an osmium ion sandwiched between two boron rings. It is qualitatively similar to Ferrocene Fe(C5H5)2 in structure and bonding however the metal-ring bonding is much stronger in this sandwich compound.
This synthesis of the first carbon-free inorganic sandwich compound is a fundamental advancement in chemistry because it expands the concept beyond organometallic to inorganometallic and thus the beginning of a new field of inorganometallic chemistry.
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References:
- Heinze K. and Lang H. , 2013. Ferrocene—Beauty and Function. Organometallics. Vol 32/Issue 20 DOI: https://doi.org/10.1021/om400962w
- Mohapatra et al. 2026. [Os(η5-B5H10)2]: A carbon-free analog of ferrocene. Science. 23 April 2026. Vol 392, Issue 6796 pp. 411-414. DOI: https://doi.org/10.1126/science.aed9192
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2] (which is an osmium ion sandwiched between two boron rings) is a fundamental advancement in chemistry because it expands the concept beyond organometallic to inorganometallic. This was sought by chemists for seven decades since discovery of Ferrocene Fe(C5H5)2 in 1951. Ferrocene has a symmetrical sandwich structure where a central iron atom placed between two flat C5H5 rings is bound (by the two carbon rings) through delocalised π electrons.){kind=link}