Size Effects of the Anions in the Ionothermal Synthesis of Carbon Nitride Materials

This is the pre-peer review data set for the manuscript "Size Effects of the Anions in the Ionothermal Synthesis of Carbon Nitride Materials". 

Semiconducting carbon nitride polymers are used in metal-free photocatalysts and in opto-electronic devices. Conventionally, they are obtained using thermal and ionothermal syntheses in inscrutable, closed systems and therefore, their condensation behavior is poorly understood. Here, we compare the synthetic protocols and properties of two types of carbon nitride materials – 2D layered poly(triazine imide) (PTI) and hydrogen-bonded melem hydrate – obtained from three low-melting salt eutectics taken from the systematic series of the alkali metal halides: LiCl/KCl, LiBr/KBr, and LiI/KI. The size of the anion plays a significant role in the formation process of the condensed carbon nitride polymers, and it suggests a strong templating effect. The smaller anions (chloride and bromide) become incorporated into triazine (C₃N₃)-based PTI frameworks. The larger iodide does not stabilize the formation of a triazine-based polymer, but instead it leads to the formation of the heptazine (C₆N₇)-based hydrogen-bonded melem hydrate as the main crystalline phase. We obtain melem hydrate as single-crystalline powders and compare it with PTI in photocatalytic hydrogen evolution from water and in an OLED device. Further, we rationalize the emergence of each carbon nitride species from its corresponding salt eutectic via density functional theory calculations. This study highlights the possibilities to further tailor the properties of eutectic salt melts for ionothermal synthesis of organic functional materials.