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

Cesium dicyanamide Cs[C 2 N 3 ] (≡ 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 ( C 2/ 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[C 2 N 3 ] are presented for the first time and the result compares well with those of NaCs 2 [C 2 N 3 ] 3 . The heat-driven cyclotrimerization process of Cs[C 2 N 3 ] was studied by thermal analyses (DSC) and temperature-dependent X-ray powder diffraction methods. At 370 °C, its trimerization product Cs 3 [C 6 N 9 ] 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 [C 6 N 9 ] 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 [C 2 N 3 ]) to their corresponding tricyanomelaminates ( A 3 [C 6 N 9 ]) with A = Li–Cs gives a basis for a discussion of the different thermal and structural characteristics.