Decades-long quest ends as scientists tame rare carbon ring once seen only in gas form

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2 days ago

Chemists at the University of Oxford have achieved a rare feat in molecular science — the synthesis of a cyclocarbon that is stable enough for spectroscopic characterisation in solution at room temperature.
The breakthrough, led by Oxford's Department of Chemistry, paves the way for in-depth studies of these unusual carbon allotropes under everyday laboratory conditions.
Until now, such rings could only be observed fleetingly under extreme environments, such as in the gas phase or at cryogenic temperatures.
The only previous example of a molecular carbon allotrope stable enough to study under normal conditions was the 1990 synthesis of fullerenes by Krätschmer and colleagues. Oxford's new work marks the first advance of its kind in over three decades.
Threaded design boosts stability
The team synthesised cyclo[48]carbon as a [4]catenane — a molecular architecture in which the C48 ring is threaded through three other macrocycles. These protective macrocycles act like molecular shields, physically blocking reactive species from reaching the delicate carbon ring.
This design, combined with the choice of a larger cyclocarbon with reduced strain, allowed the molecule to persist in solution at 20°C for an impressive 92-hour half-life.
The researchers also fine-tuned the unmasking step, which includes the transformation of a precursor molecule into the final product, to use mild conditions, further protecting the carbon ring.
Characterisation confirmed the structure using mass spectrometry, NMR, UV-visible, and Raman spectroscopy. A single intense ^13C NMR resonance from all 48 sp^1 carbon atoms revealed that each carbon occupies an equivalent environment — strong evidence for the symmetrical cyclocarbon catenane.
Years in the making
Lead author Dr Yueze Gao said: 'Achieving stable cyclocarbons in a vial at ambient conditions is a fundamental step. This will make it easier to study their reactivity and properties under normal laboratory conditions.'
For senior author Professor Harry Andersen, the result caps off more than a decade of work. 'This achievement marks the culmination of a long endeavour to synthesise cyclocarbon catenanes, based on the hope that they might be stable enough to study at room temperature,' he said.
'The original grant proposal was written in 2016, based on preliminary results from 2012–2015. It is satisfying to have reached this point, because there were many times when the goal seemed unrealistic and unachievable. This work would not have been possible without the outstanding facilities for NMR spectroscopy in the Department of Chemistry at Oxford,' Andersen added.
The research brought together expertise from multiple UK institutions, including the University of Manchester, the University of Bristol, and the Central Laser Facility at Rutherford Appleton Laboratory.
By proving that cyclocarbons can be stabilised in a bottle at room temperature, the work opens the door to exploring their chemical reactivity, optical behaviour and potential technological applications.
For a class of molecules once thought too reactive to tame, Oxford's cyclocarbon catenane may be just the beginning of a new chapter in carbon chemistry.
The findings have been published in the journal Science.
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