Single crystal structure refinement and physical characterization of the 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate)diammonium salt (ABTS)

2,2'-Azinobis(3-ethylbenzothiazoline-6-sulfonate), ABTS, has been studied by X-ray crystallography and its structure solved from single crystal diffraction data. The title compound has monoclinic symmetry and belongs to the P21/c space group. Cell parameters are: a=0.8707(1), b=3.6843(7), and c=0.8222(1) nm, beta=97.18(3)degrees with four formula units per crystalline cell. The structure is built of two types of pseudo-planar molecules. ABTS crystallizes with two very labile water molecules as demonstrated from the structural determination and supported by infrared and thermogravimetric analyses. From the structural determination and the calculated spin density matrix, it is possible to explain the complex ESR behavior of ABTS and its intercalated derivatives previously observed in the solid state. Changes in ESR spectra with temperature mainly arise from water molecule removal, and not from molecular deformations or thermally activated electron transfers.