Molecular Heptazine–Platinum Complexes to Model Metal–Support Coordination in Platinized Graphitic Carbon Nitride: Insights into Catalyst Stability and Support Suitability

Abstract Solid support materials are crucial in heterogeneous catalysis for stabilizing active metallic species. Among potential support materials, heptazine-based “graphitic carbon nitride” or “gC3N4” has received significant research attention due to its abundant nitrogen sites, which are widely hypothesized to anchor catalytic metals through direct coordination. To better understand such a complexation mode while circumventing the structural complexity of gC3N4 materials, we employed as molecular models the heptazine compounds melem, cyamelurate, and melonate, with which we attempted Pt–heptazine complexation to emulate the interactions between the terminations and defects of gC3N4 with platinum, an important catalytic species. Despite extensive characterizations, only second-sphere coordination could be verified, while primary-sphere platinum-heptazine complexation could not be unambiguously observed, suggesting that such interactions may be intrinsically weak under the investigated conditions. These findings from model systems imply that gC3N4 materials may exhibit weaker-than-expected coordinative stabilization. Consistent with this implication, a series of Pt–gC3N4 composites evaluated as catalysts in nitrobenzene transfer hydrogenation exhibited platinum leaching more severely compared to a benchmark Pt–TiO2. Beyond providing molecular-level insights into gC3N4 supports, the methodology of the model compound presented here offers a useful framework for investigating interfacial coordinative interactions in support materials.