Spiro-Carbon: A Metallic Carbon Allotrope Predicted from First Principles Calculations.

A structurally stable microporous metallic carbon allotrope, poly(spiro[2.2]penta-1,4-diyne) or, for short, spiro-carbon, with I4 /amd (D ) symmetry is predicted by first-principles calculations using density functional theory (DFT). The calculations of electronic, vibrational, and structural properties show that spiro-carbon has lower relative energy than other elusive carbon allotropes such as T-Carbon and 1-diamondyne (Y-Carbon). Its structure can be pictured as a set of trans-cisoid-polyacetylene chains tangled and interconnected together by sp carbon atoms. Calculations reveal a metallic electronic structure arising from an "intrinsic doping" of trans-cisoid-polyacetylene chains with sp carbon atoms. Possible synthetic routes and various simulated spectra (XRD, NMR, and IR absorption) are provided in order to guide future efforts to synthesize this novel material.