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

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.