By the reaction of solid As4S4 with gaseous Br2 at a temperature of 410 K gaseous AsSBr and AsS2Br are formed; the reaction with gaseous I2 at 468 K leads to the formation of AsSI, AsS2I, As2S2I2 and As2S3I2. Thermodynamic data on these novel species are obtained by mass spectrometry. The experimental findings are extended and confirmed by ab initio quantum chemical calculations. Undoubtedly the molecules AsSX (X = Br, I) and As2S2I2 contain As-atoms in the formal oxidation state III. Unexpectedly, in AsS2X arsenic is not of formal oxidation state +V but +III: due to the absence of As–S π-bonding, the molecular structure of AsS2X is arranged as a dithia-arsirane with an AsS2 three-membered ring. For comparison with AsS2X, PS2Br is investigated for the first time. This high temperature species is planar with symmetry C2v and phosphorus of the formal oxidation state +V in which the two PS π-bonds are realized due to their strength over one S–S σ-bond. As2S3I2 contains a five-membered As2S3-ring with one S–S-bond. The ionization energies are determined and compared with those obtained from calculations; they serve as a further indication for the structures realized in these molecules.
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