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Biphenylene network: A nonbenzenoid carbon allotrope

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Science  21 May 2021:
Vol. 372, Issue 6544, pp. 852-856
DOI: 10.1126/science.abg4509

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Biphenylene carbon sheets

Although graphene forms two-dimensional carbon sheets, other arrangements of carbon rings could also assemble as flat sheers. Fan et al. synthesized an ultraflat biphenylene carbon sheet consisting of sp2-hybridized carbon atoms forming four-, six-, and eight-membered rings on a gold surface. An adsorbed halogenated terphenyl molecule undergoes a two-step interpolymer dehydrofluorination polymerization that creates the four- and eight-membered rings through carbon–carbon bond formation. Scanning tunneling spectroscopy revealed that this carbon allotrope is metallic.

Science, abg4509, this issue p. 852

Abstract

The quest for planar sp2-hybridized carbon allotropes other than graphene, such as graphenylene and biphenylene networks, has stimulated substantial research efforts because of the materials’ predicted mechanical, electronic, and transport properties. However, their syntheses remain challenging given the lack of reliable protocols for generating nonhexagonal rings during the in-plane tiling of carbon atoms. We report the bottom-up growth of an ultraflat biphenylene network with periodically arranged four-, six-, and eight-membered rings of sp2-hybridized carbon atoms through an on-surface interpolymer dehydrofluorination (HF-zipping) reaction. The characterization of this biphenylene network by scanning probe methods reveals that it is metallic rather than a dielectric. We expect the interpolymer HF-zipping method to complement the toolbox for the synthesis of other nonbenzenoid carbon allotropes.

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