THE CRYSTAL-STRUCTURE AND OPTICAL-ACTIVITY OF POTASSIUM DITHIONATE, K2S2O6

The absolute chirality of potassium dithionate, K2S2O6, M(r) = 238.3, trigonal, space group P321, a = 9.782(1) Angstrom, c = 6.298(2) Angstr om, V = 521.9(1) Angstrom(3), Z = 3, R = 0.024, wR = 0.031 for 2586 un ique observed reflections, has been determined at room temperature thr ough a combination of single-crystal x-ray diffraction, including anom alous scattering, and optical study. Using a classical point dipole-di pole theory, good agreement has been obtained between the calculated a nd observed optical activity and refractive indices at room temperatur e (rho = -6.57 degrees mm(-1) along [001], n(e) = 1.512, n(0) = 1.453 at a wavelength of 632.8 nm). The polarizabilities of the different at oms have also been determined by means of this theory. It has been fou nd that in order to fit the optical data, it is necessary that the oxy gen atoms must show quite large anisotropic polarizabilities. The stru ctural features responsible for the optical rotation have been identif ied. In this way, a visual correlation between the sign of the optical activity and the arrangement of atoms in the crystal structure has be en established.