Acta Crystallographica Section B

Structural Science

Volume 60, Part 2 (April 2004)

Acta Cryst. (2004). B60, 155-162 [doi:10.1107/S0108768104003325]

The surprisingly elusive crystal structure of sodium metabisulfite

K. L. Carter, T. A. Siddiquee, K. L. Murphy and D. W. Bennett

Abstract: The crystal structure of Na₂S₂O₅, a simple and common ionic compound, is reported here for the first time. The crystals form non-merohedral twins, with the twin domains related by a twofold axis which bisects the angle between the a and c axes of each unit cell. The structure was determined from a single-crystal fragment of a twinned crystal that had undergone cleavage along the twin boundary. In addition to the problems associated with twinning, space-group determination proved difficult as well, with the structure initially determined in the P2₁ space group appearing to be disordered with two rotational conformers of the metabisulfite ion occupying equivalent sites in the lattice. An analysis at low temperature provided new weak reflections which were inconsistent with the original unit cell, but indexed to the correct unit cell, allowing for space group and crystal structure determination. The apparent structure, which appeared disordered in P2₁, seems to have resulted from an apparently fortuitous superposition of two conformationally inequivalent S₂O $_5^{2-}$ anions in the asymmetric unit of the correct structure in the P2₁/n space group. The metabisulfite ions in this structure do not adopt the C_s geometry observed in previously determined crystal structures containing S₂O $_5^{2-}$ . The structures of both ions in the asymmetric unit are effectively conformational mirror images of one another with two of the O atoms on each S atom in the ion approaching an eclipsed geometry. This observation provides further evidence that the structures of sulfur-oxy anions in the solid state are dictated mainly by interionic coulombic forces rather than by intraionic bonding interactions

Online 18 March 2004


	Structure factor file (CIF format) (33.2 kbytes) Contains datablock metabi_P21

	Structure factor file (CIF format) (95.3 kbytes) Contains datablock metabi_P21_n

Notes:

To open or display or play some files, you may need to set your browser up to use the appropriate software. See the full list of file types for an explanation of the different file types and their related mime types and, where available links to sites from where the appropriate software may be obtained.

The download button will force most browsers to prompt for a file name to store the data on your hard disk.

Where possible, images are represented by thumbnails.