The dithiolate complex [1,5-bis(mercaptoethyl)-1,5-diazacyclooctane]Pd(II), (bme-daco)Pd-II or Pd-1, whose structure was determined by X-ray crystallography (monoclinic P2(1)/m space group with a = 6.1680(10) Angstrom, b = 15.715(5) Angstrom, c = 6.5930(10) Angstrom, beta = 107.090(10)degrees, Z = 2, R = 0.0291, R(W) = 0.0718), has been added to a group of metal thiolates which form sulfur-site SO2 adducts. Exposure of the Pd-l complex to SO2 in methanol results in the precipitation of yellow/orange crystalline Pd-1 SO2 : monoclinic space group, P2(1)/c (No. 14), with a 8.928(2) Angstrom, b = 14.655(4) Angstrom, c = 11.067(2) Angstrom, beta = 97.29(2)degrees, Z = 4, R = 0.0348, R(W) = 0.0944. Analogous thiolate-SO2 adducts based on (bme-daco)Ni-II, Ni-1 . SO2, (Ph(2)PCH(2)CH(2)S)(2)Ni-II, Ni-2 . SO2, and (bme*-daco)Ni-II, Ni-1*. SO2, also precipitate from methanol. To explore the transformation of SO2 to SO42- in these adducts, the following three factors expected to control the sulfate-forming reaction have been examined : (i) the stability of SO2 adducts; (ii) the oxidizability of the metal thiolate or its tendency to generate disulfide products on oxidation; and (iii) the ability of the metal thiolates to react with O-2 and produce sulfur-oxygenated products. The studies indicate that the last factor is the most important influence on SO2 oxygenation. A possible mechanism involves the transient formation of an SO2-stabilized sulfperoxide intermediate, which behaves as a nucleophile and further reacts with SO2 to produce SO42-. The use of the aforementioned metal thiolate complexes as catalysts for SO2 oxygenation in the presence of a sacrificial electron donor has also been explored; simple salts such as NiCl2 and NiSO4 are more efficient than the complexes.