Potassium melonate, K3[C6N7(NCN)3]·5H2O, and its potential use for the synthesis of graphite-like C3N4 materials

Melonates, Mx3/x[C6N7(NCN)3], contain the aromatic and planar tricyanamino-s-heptazine anion. Only one example, the potassium derivative, has been isolated in pure form so far, but it has never been characterised comprehensively. Potassium melonate is obtained from a reaction of the polymer melon, [C6N9H3]n, with KSCN. 13C NMR, FTIR, Raman, UV-vis and luminescence spectroscopy support the proposed molecular structure. The crystal structure of the hydrate K3[C6N7(NCN)3]·5H2O was determined by single crystal X-ray analysis (MoKα: Pbca (no. 161), a = 6.538(2), b = 24.033(6), c = 23.684(6) Å and Z = 8). Thermogravimetric analysis shows that the dehydrated salt starts to decompose at temperatures above 500 °C. The [C6N7(NCN)3] unit is an ideal molecular building block for carbon(IV) nitrides, especially s-heptazine based graphite-like C3N4 networks.