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

Cesium dicyanamide Cs[C₂N₃] (≡ 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, β = 110.803(3)° at −70 °C and a = 939.59(7), b = 1281.58(8), c = 827.57(6) pm, β = 110.610(3)° at 20 °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 °C, its trimerization product Cs₃[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 (Cs₃[C₆N₉] or Cs₃[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 (A₃[C₆N₉]) with A = Li–Cs gives a basis for a discussion of the different thermal and structural characteristics. [ABSTRACT FROM AUTHOR]