A series of nickel(II) complexes containing sulfinate and sulfenate S-donor sites has been prepared from systematic oxygenations of the dithiolate complex [1,5-bis(2-mercapto-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II) ((bme*-daco)Ni, 1*) and the whole series characterized by mass spectrometry : and X-ray crystallography. The dithiolate complex reacts in organic solvents with molecular oxygen to produce sulfinate (NiS(O)(2)R) complexes, while reactions with hydrogen peroxide have, in addition,permitted the isolation of sulfenate (NiS(O)R) products. The X-ray crystal structures of the complexes [1-(2-mercapto-2-methylpropyl)-5-(2-sulfino-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II) (2*), [1,5-bis(2-sulfino-2-methylpropyl)-1,5-diazacyclootanato-(2-)]nickel(II)) (3*), [1,5-bis(2-sulfeno-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II) (5*), and [1-(2-sulfeno-2-methylpropyl)-5-(2-sulfino-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II) (6*) were determined and metric data compared with previously characterized 1* and 4*, [1-(2-mercapto-2-methylpropyl)-5-(2-sulfeno-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II). : and X-ray crystallography. The dithiolate complex reacts in organic solvents with molecular oxygen to produce sulfinate (NiS(O)(2)R) complexes, while reactions with hydrogen peroxide have, in addition,permitted the isolation of sulfenate (NiS(O)R) products. The X-ray crystal structures of the complexes [1-(2-mercapto-2-methylpropyl)-5-(2-sulfino-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II) (2*), [1,5-bis(2-sulfino-2-methylpropyl)-1,5-diazacyclootanato-(2-)]nickel(II)) (3*), [1,5-bis(2-sulfeno-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II) (5*), and [1-(2-sulfeno-2-methylpropyl)-5-(2-sulfino-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II) (6*) were determined and metric data compared with previously characterized 1* and 4*, [1-(2-mercapto-2-methylpropyl)-5-(2-sulfeno-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II). : and X-ray crystallography. The dithiolate complex reacts in organic solvents with molecular oxygen to produce sulfinate (NiS(O)(2)R) complexes, while reactions with hydrogen peroxide have, in addition,permitted the isolation of sulfenate (NiS(O)R) products. The X-ray crystal structures of the complexes [1-(2-mercapto-2-methylpropyl)-5-(2-sulfino-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II) (2*), [1,5-bis(2-sulfino-2-methylpropyl)-1,5-diazacyclootanato-(2-)]nickel(II)) (3*), [1,5-bis(2-sulfeno-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II) (5*), and [1-(2-sulfeno-2-methylpropyl)-5-(2-sulfino-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II) (6*) were determined and metric data compared with previously characterized 1* and 4*, [1-(2-mercapto-2-methylpropyl)-5-(2-sulfeno-2-methylpropyl)-1,5-diazacyclooctanato(2-)]nickel(II).