The cumulenic linear C<sub>5</sub> and its coupling-reaction products.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 41107270.
- Also identified by DOI 10.1038/s41467-025-64310-4 and PMC identifier 12534424.
- Licence recorded as CC BY-NC-ND.
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Abstract
Linear carbon (C<sub>n</sub>), an elusive sp-hybridized carbon allotrope, has long attracted interest for its remarkable properties and debated structures. Here, we report the synthesis of an uncapped linear C<sub>5</sub> via tip-induced dehalogenation and ring-opening reaction of C<sub>5</sub>Br<sub>6</sub>, with its cumulenic structure confirmed by atomic force microscopy. We further demonstrate the tip-induced coupling of linear C<sub>5</sub> to form longer chains (e.g., C<sub>10</sub>, C<sub>15</sub>). By applying higher voltage pulses to C<sub>5</sub>Br<sub>6</sub> (also C<sub>6</sub>Br<sub>6</sub>), various carbon chains, including C<sub>9</sub>, C<sub>10</sub>, C<sub>13</sub>, C<sub>14</sub>, C<sub>15</sub>, C<sub>17</sub>, C<sub>18</sub>, C<sub>21</sub>, C<sub>23</sub>, could be synthesized. Even-numbered chains (C<sub>10</sub>, C<sub>14</sub> and C<sub>18</sub>) adopt polyynic structures due to a Peierls transition on NaCl, whereas for odd-numbered chains, C<sub>9</sub> adopts a cumulene-like structure, and longer ones exhibit hybrid structures with terminal triple bonds and cumulene-like interiors. Scanning tunneling spectroscopy reveals smaller transport gaps for odd- than even-numbered chains, consistent with Peierls theory, and decreasing gaps with increasing chain length.