SO2 solutions of azide anions are bright yellow, and their Raman spectra indicate the presence of covalently bound azide. Removal of the solvent at -64 degreesC from CsN3 or N(CH3)(4)N-3 solutions produces yellow (SO2)(2)N-3- salts. Above -64 degreesC, these salts lose 1 mol of SO2, resulting in white SO2N3- salts that are marginally stable at room temperature and thermally decompose to the corresponding azides and SO2. These anions were characterized by vibrational and N-14 NMR spectroscopy and theoretical calculations. Slow loss of the solvent by diffusion through the walls of a sealed Teflon tube containing a sample of CsSO2N3 in SO2 resulted in white and yellowish single crystals that were identified by X-ray diffraction as CsSO2N3.CsSO3N3 with a = 9.542(2) Angstrom, b = 6.2189(14) A, c = 10.342(2) Angstrom, and beta = 114.958(4)degrees in the monoclinic space group P2(1)/m, Z = 2, and Cs2S2O5.Cs2S2O7.SO2, respectively. Pure CsSO3N3 was also prepared and characterized by vibrational spectroscopy. The S-N bond in SO2N3- is much weaker than that in SO3N3-, resulting in decreased thermal stability, an increase in the S-N bond distance by 0.23 Angstrom, and an increased tendency to undergo rotational disorder. This marked difference is due to SO3 being a much stronger Lewis acid (pF(-) value of 7.83) than SO2 (pF(-) value of 3.99), thus forming a stronger S-N bond with the Lewis base N-3(-). The geometry of the free gaseous SO2N3-anion was calculated at the RHF, MP2, B3LYP, and CCSD(T) levels. The results show that only the correlated methods correctly reproduce the experimentally observed orientation of the SO2 group.