TRIMERIZATION OF DICYANAMIDE IONS C2N3- I N THE SOLID - SYNTHESES, CRYSTAL-STRUCTURES, AND PROPERTIES OF NACS2(C2N3)(3) AND NA3C6N9-CENTER-DOT-3H(2)O

The Tricyanomelaminate Na3C6N9 . 3H(2)O is obtained by heating NaC2N3 to 500 degrees C and subsequent crystallization from water. According to the single-crystal structure determination (Na3C6N9 . 3H(2)O: P62c; a = 1023.53(8), c = 650.85(15) pm, Z = 2, R1 = 0.0276, wR2 = 0.0710) in the solid cyclic C6N93- ions occur. Partial ion exchange and crysta llization from water yields anhydrous NaCs2(C2N3)(3). The X-ray struct ure determination (NaCs2(C2N3)3: P6(3)/m, a = 700.01(4), c = 1449.29(7 ) pm, Z = 2, R1 = 0.0173, wR2 = 0.0432) reveals C2N3-ions in the solid . Calorimetric investigations and detailed IR spectroscopy of NaC2N3, Na3C6N9, Na3C6N9 . 3 H2O, as well as NaCs2(C2N3)(3) reveal in combinat ion with the structure analyses that NaC2N3 transforms to Na3C6N9 abov e 380 degrees C by trimerization of the C2N3- ions in the solid. Above 180 degrees C the hydrate Na3C6N9 . 3H(2)O reversibly dehydrates.