The structure of sodium dithionite and the nature of the dithionite ion

The structure of sodium dithionite has been determined by X-ray analysis. The crystals are monoclinic, a----6"404:k0.0045, b----6-559~:0.0028, c----6"586:k0-0056 /~, fl---119 31':k0 02 ', space group P2/c, with two molecules of Na2S204 in the unit cell. The structure was refined by successive difference Fourier projections on (001), ( The anion consists of two SO~-units, joined by a very long S-S bond (2.39 /~), in an eclipsed configuration with the planes of opposite SO~groups only 30 from parallel. It has approximate C~.r symmetry. The sodium coordination is of an unusual type. The electronic structures of SO2, SO~-, and -O2S-SO~-are discussed.