Bottom-Up Synthesis of Schwarzite Carbon Allotropes from Heptagon Carbon Cycles

Schwarzites represent a class of theoretical carbon allotropes defined by their continuous, negatively curved surfaces exhibiting three-dimensional periodicity. These hypothetical materials are garnering considerable interest due to their projected high surface area to volume ratio, substantial porosity, tunable electrical conductivity, and exceptional mechanical strength paired with low density. Despite over thirty years of research, attempts to synthesize Schwarzites from gas-phase carbon atoms were not successful and the focus is shifting to other methods, such as zeolite templating and bottom-up synthesis.
The design of new Schwarzite structures involves the placement of sp2-carbon polygon tiles on mathematically defined triply periodic minimal surfaces. Until recently, Schwarzite designs were dominated by using octagons. In this work, Schwarzite tiling with heptagons will be done for the convenience of the bottom-up synthesis and it will be systematically analyzed and classified by symmetry and topology. For the first time, detailed methodologies for the bottom-up synthesis of various Schwarzites representing gyroid, P, D, CLP, IWP, H, HT, and GW surfaces will be provided, with a trimer of heptagons identified as the central building block in most synthetic approaches. The shift in the synthetic design paradigm lies in creating benzene rings between heptagon rings by connecting pairs of heptagon vertices in a [2+2+2] cyclization as opposed to the current approach for making negatively curved nanographenes by using benzene rings as building blocks.
The bottom-up synthesis using strategically chosen heptagon trimers offers superior control over topology, geometry, and pore size distribution in periodic carbon materials compared to zeolite templating. This approach holds significant potential for advancing the design and functionality of carbon-based structures.