Top view (top) and side view (bottom) of penta-graphane. Yellow and blue spheres show two types of carbon atoms, while red balls correspond to hydrogens.[1]
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PG
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Penta-graphene is a hypothetical carbon allotrope composed entirely of carbon pentagons and resembling the Cairo pentagonal tiling.[2] Penta-graphene was proposed in 2014 on the basis of analyses and simulations.[2] Further calculations predicted that it is unstable in its pure form,[3] but can be stabilized by hydrogenation.[1] Due to its atomic configuration, penta-graphene has an unusually negative Poisson’s ratio and very high ideal strength believed to exceed that of a similar material, graphene.[2]
Penta-graphene contains both sp2 and sp3 hybridized carbon atoms. Contrary to graphene, which is a good conductor of electricity, penta-graphene is predicted to be an insulator with an indirect band gap of 4.1–4.3 eV. Its hydrogenated form is called penta-graphane. It has a diamond-like structure with sp3 and no sp2 bonds, and therefore a wider band gap (ca. 5.8 eV) than penta-graphene.[1] Chiral penta-graphene nanotubes have also been studied as metastable allotropes of carbon.[4][2][5]