Fig. 1. CNCO samples synthesized by hydrothermal method

Fig. 2. Structure of molecular crystal CNCO. (a) Clusters formed by hydrogen-bonded linkages of melamine and cyanuric molecules; (b) schematic representation of the monolayer structure of a CNCO crystal; (c) schematic representation of the structure of a CNCO crystal along the b-axis direction

Fig. 3. Analysis of hydrogen bonding and weak interactions in CNCO. (a) Differential charge densities; (b) Hirshfeld surface centered on cyanuric acid; (c) proportion of contact areas for different interactions on the Hirshfeld surfaces; (d) N—H…O hydrogen bonding fingerprints; (e) N—H…N hydrogen bonding fingerprints; (f) π-π stacking fingerprints

Fig. 4. Structure characterizaion of CNCO. (a) XRD sepctra of CNCO powder; (b) comparison of infrared absorption peak positions of N—H bond stretching vibrations in melamine crystal and CNCO

Fig. 5. Optical properties of CNCO. (a) UV-visible-near infrared diffuse reflectance spectrum, where the inset shows UV absorption band gap; (b) theoretical refractive index dispersion curve

Fig. 6. Electronic properties of CNCO obtained via first principles calculations. (a) Band structure; (b) density of states; (c) electron density map at the top of valence band; (d) electron density map at the bottom of conduction band