The crystal structure and the absolute configuration of a-NiSOa.6H20 (Mr = 26286) have been determined by X-ray diffraction at room temperature. For a crystal that is optically laevo at 0.4579 ixm, laevo at 0-4765 i~m and dextro at 0-5145 lxm, the space group was found to be P4~2~2 (D4), with a= 6.783(1), c=18.288 (2) A, V=841.4(3) A 3, Z=4, Dx = 2.075 Mg m -3, Mo Ka, A = 0.71069 A, /z = 2.58 mm -t, F(000)= 544. The structure was refined to R =0.0254 and Re =0.0327 for 1864 reflections. The chiral arrangement of O atoms in the structure is examined in connection with the theory of Glazer & Stadnicka [J. Appl. Cryst. (1986), 19, 108-122] and linked with the measured optical rotation at wavelengths below -0.5 lxm and above -2.0 ixm. It is shown that the contribution from the O atoms of the water of crystallization is more important than that from the sulfate O atoms in determining this part of the optical rotatory dispersion, whereas the observed anomalies between these wavelengths are principally due to d-d transitions in the nickel ion. Calculations using the program of Devarajan & Glazer [Acta Cryst. (1986), A42, 560-569] support this view.
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Stadnicka et al. (1987) studied this question.