Carbon Di-carbene Allotrope as a Zero- Dimensional Carbon Platform for Small-Molecule Activation and Nitrogen-to-Ammonia Conversion

Abstract Carbon allotropes span molecular to extended architectures, with dimensional-ity playing a central role in determining their electronic structure and chemical reactivity. Inspired by the unique electronic characteristics of carbenes and the functional diversity of carbon allotropes, we computationally design a previously unexplored zero-dimensional carbon dicarbene allotrope (CDCA) at the ωB97XD/Def2-TZVP level. CDCA is composed exclusively of carbon atoms and incorporates two electronically communicating carbene centres within a cyclic molecular framework. Density-of-states analysis and ab initio molecular dynamics simulations are employed to characterize its electronic structure, reactive sites, and structural stability. The singlet state is substantially more stable than the triplet state, while the carbon framework remains structurally stable during the investigated finite-temperature dynamics. CDCA exhibits pronounced reactivity toward SO 2 , SO 3 , NO, NO 2 , CO, CO 2 , and H 2 O through interactions involving its two carbene centres. Most notably, the two-centre architecture enables orientation-dependent activation of molecular nitrogen: interaction of N 2 with both carbene centres promotes N–N bond cleavage, whereas single-centre interaction yields an intact N 2 adduct. Subsequent stepwise hydrogenation of the activated nitrogen species provides a calculated pathway toward NH 3 formation. These results establish CDCA as a distinct zero-dimensional, carbon-only molecular architecture in which intrinsic carbene reactivity is integrated into a carbon allotrope, providing a new conceptual framework for small-molecule activation and the exploration of carbon-only systems for nitrogen chemistry.