The reaction of [(Me3Si)(2)N](2)S with equimolar amounts of SCl2 and SO2Cl2 produces S4N4 in a good yield. The new chalcogen nitride 1,5-Se2S2N4 has been prepared in high yield by two different reactions: (a) from [(Me3Si)(2)N](2)S and SeCl4 and (b) from [(Me3Si)(2)N](2)Se with equimolar amounts of SCl2 and SO2Cl2. 1,5-Se2S2N4 has a cage structure similar to those of S4N4 and Se4N4. The crystal structure is disordered with site occupation factors ca. 50% for selenium in each chalcogen atom position. The 12 eV EI mass spectrum shows Se2SN2+ as the fragment with highest mass. Both the N-14 and Se-77 NMR spectra show a single resonance (-238 and 1418 ppm, respectively). These data rule out the possibility that the crystalline sample is a solid solution of S4N4 and Se4N4 and imply the presence of 1,5-Se2S2N4. This deduction was further verified by Raman spectroscopy and vibrational analysis.