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 (Li(3)[C(6)N(7)O(3)].6H(2)O; Na(3)[C(6)N(7)O(3)].4.5H(2)O; K(3)[C(6)N(7)O(3)].3H(2)O; Rb(3)[C(6)N(7)O(3)].3H(2)O) are presented. Thermogravimetric analysis shows that the dehydrated salts start to decompose at temperatures above 500 degrees 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 M(3)[C(3)N(3)O(3)]. The photoluminescence spectra indicate a very strong solid state UV-emission with maxima between 280 and 400 nm.