Sensing of sulfur dioxide by base metal thiolates: structures and properties of molecular NiN2S2/SO2 adducts.

The cis-dithiolate N2S2Ni complex bismercaptoethanediazacycloheptanenickel(II), (bme-dach)Ni or Ni-1', takes up two equivalents of sulfur dioxide in which thiolate-sulfur to SO2-sulfur interactions are well-defined by X-ray crystallography. Ni-1' x 2SO2, C9H18N2NiO4S4, yields monoclinic crystals belonging to the P2(1)/c space group: a = 10.308(4) angstroms, b = 13.334(5) angstroms, c = 10.842(4) angstroms, alpha = 90 degrees, beta = 91.963(6) degrees, gamma = 90 degrees, and Z = 4. Further characterization by nu(SO) IR spectroscopy, thermal gravimetric analysis, electronic spectroscopy, and visual color changes upon reversible SO2 adduct formation establish Ni-1' and the analogous bismercaptoethanediazacyclooctane derivative, (bme-daco)Ni, Ni-1, to be viable candidates for technical development as chemical sensors of this noxious gas. Visual SO2 detection limits of Ni-1 and Ni-1' are established at 25 and 100 ppm, respectively. Both the Ni-1' x 2SO2 adduct and the Ni-1' reactant are air stable. In addition, the stability of Ni-1' x SO2 to vacuum and removal of SO2 by heating make Ni-1' a possible storage/controlled release complex for SO2 gas.