From Cs[C₂N₃] to Cs₃[C₆N₉] - a thermal and structural investigation

Cesium dicyanamide Cs[C2N3] (equivalent to Cs[N(CN)(2)] or Cs[dca]) was obtained by a metathesis reaction in form of transparent colorless platelets. The results of single-crystal X-ray structure measurements and refinements (C2/c, Z = 8) with the monoclinic cell parameters a = 932.31(8), b = 1274.67(9), c = 824.94(7) pm, beta = 110.803(3)degrees at -70 degrees C and a = 939.59(7), b = 1281.58(8), c = 827.57(6) pm, beta = 110.610(3)degrees at 20 degrees C corroborate earlier results for this compound. The Raman and IR spectra of Cs[C2N3] are presented for the first time and the result compares well with those of NaCs2[C2N3](3). The heat-driven cyclotrimerization process of Cs[C2N3] was studied by thermal analyses (DSC) and temperature-dependent X-ray powder diffraction methods. At 370 degrees C, its trimerization product Cs-3[C6N9] is formed, crystallizing in the orthorhombic space group Pbam with the cell parameters a = 3043.0(3), b = 1052.4(1) and c = 415.21(4) pm for Z = 4. The IR spectrum of this cesium tricyanomelaminate (Cs-3[C6N9] or Cs-3[TCM]) is presented, but a well-resolved Raman spectrum could not be acquired owing to fluorescence phenomena. An overview about the cyclotrimerization reactions of all pseudo-binary alkali-metal dicyanamides (A[C2N3]) to their corresponding tricyanomelaminates (A(3)[C6N9]) with A = Li-Cs gives a basis for a discussion of the different thermal and structural characteristics.