During the past decade we have discovered the rich chemistry of the sulfur/selenium iodine and sulfur/selenium bromine cations, examples of which include S7I+, (S7I)2I3+, M2I4(2+), 1 (Se6I+)n, Se6I2(2+),S7Br+, Se2Br5+, and M3Br3+2(M = S,Se)3. These cations maximize positive charge delocalization giving rise to thermodynamically stable pi bonds and have in many cases cluster-like geometries.3 In contrast, except for MCl3+ (M = S, Se),4,5 the only example of a sulfur/selenium chlorine cation to be unambiguously characterized is Se9Cl+,6 although Raman evidence has been presented for the unstable S7Cl+ cation.7 In addition, S2Cl3+ and Se2Cl3+ have been claimed in solution8a and SCl+ has been claimed in the solid state.8b The evidence suggested that lower sulfur and selenium/chlorine cations were less stable than their bromo and iodo analogues and might only exist as reactive intermediates. However, we have succeeded in preparing S3-Cl3AsF6 and Se3Cl3AsF6, containing the first example of M3Cl3+ cations, by the reaction of MCl3AsF6 and M (M = S, Se) using sulfur dioxide as solvent. The syntheses and the characterizations of these cations are the subject of this brief communication. The salt Se3Cl3AsF6 was prepared according to eq 1 by the reaction of SeCl3AsF6 (0.466 g, 1.24 mmol) and selenium (0.197 g, 2.44 mmol) in liquid sulfur dioxide, SO2 (5.67 g), in a two-bulb glass vessel.9 After 6 h of stirring at room temperature, addition of sulfuryl chloride fluoride, SO2ClF (0.8 g), and slow removal Reactions of stoichiometric quantities of SCl3AsF6 and sulfur, or SeCl3AsF6 and selenium, in liquid sulfur dioxide lead to the quantitative syntheses of crystalline ClM+(Cl)MMCl(AsF6-) (M = S, Se), containing the first M3Cl3+ cations. The compounds were characterized by single-crystal X-ray diffraction and FT-Raman spectroscopy.