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Synchrotron X-ray Electron Density Analysis of Chemical Bonding in the Graphitic Carbon Nitride Precursor Melamine

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DOI

Melamine is a precursor and building block for graphitic carbon nitride (g-CN) materials, a group of layered materials showing great promise for catalytic applications. The synthetic pathway to g-CN includes a polycondensation reaction of melamine by evaporation of ammonia. Melamine molecules in the crystal organize into wave-like planes with an interlayer distance of 3.3 Å similar to that of g-CN. Here we present an extensive investigation of the experimental electron density of melamine obtained from modelling of synchrotron radiation X-ray single-crystal diffraction data measured at 25 K with special focus on the molecular geometry and intermolecular interactions. Both intra- and interlayer structures are dominated by hydrogen bonding and π-interactions. Theoretical gas-phase optimizations of the experimental molecular geometry show that bond lengths and angles for atoms in the same chemical environment (C−N bonds in the ring, amine groups) differ significantly more for the experimental geometry than for the gas-phase-optimized geometries, indicating that intermolecular interactions in the crystal affects the molecular geometry. In the experimental crystal geometry, one amine group has significantly more sp 3-like character than the others, hinting at a possible formation mechanism of g-CN. Topological analysis and energy frameworks show that the nitrogen atom in this amine group participates in weak intralayer hydrogen bonding. We hypothesize that melamine condenses to g-CN within the layers and that the unique amine group plays a key role in the condensation process.

Original languageEnglish
Article numbere202201295
JournalChemistry - A European Journal
Volume28
Issue54
Number of pages11
ISSN0947-6539
DOIs
Publication statusPublished - Sep 2022

    Research areas

  • chemical bonding, electron density, graphitic carbon nitride, melamine, synchrotron X-ray diffraction, EXPERIMENTAL CHARGE-DENSITY, CRYSTAL-STRUCTURE, NEUTRON-DIFFRACTION, SCATTERING FACTORS, MODEL ENERGIES, WAVE-FUNCTIONS, REFINEMENT, ACCURATE, 2,4,6-TRIAMINO-S-TRIAZINE, CRYSTALEXPLORER

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