Alkalicyamelurates, M3[C6N7O3]·xH2O, M = Li, Na, K, Rb, Cs: UV-luminescent and thermally very stable ionic tri-s-triazine derivatives

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Abstract
Cyamelurates are salts of cyameluric acid, a derivative of tri-s-triazine (1,3,4,6,7,9-hexaazacyclo[3.3.3]azine or s-heptazine). These compounds are thermally very stable and possess interesting structural and optical properties. Only very few tri-s-triazine derivatives have been reported in the literature. The water-soluble alkali cyamelurates were extensively characterized using NMR, FTIR, Raman, UV, luminescence spectroscopy and elemental analysis. In addition, the single crystal X-ray structure analyses of the four hydrates of lithium, sodium, potassium and rubidium cyamelurates (Li3[C6N7O3]·6H2O; Na3[C6N7O3]·4.5H2O; K3[C6N7O3]·3H2O; Rb3[C6N7O3]·3H2O) are presented. Thermogravimetric analysis shows that the dehydrated salts start to decompose at temperatures above 500 °C. The thermal stability does not depend on the cations which is in contrast to the analogous s-triazine salts, i.e. the alkali cyanurates M3[C3N3O3]. The photoluminescence spectra indicate a very strong solid state UV-emission with maxima between 280 and 400 nm.