Biaxial tensors for anomalous scattering of X-rays in selenolanthionine

X-ray pleochroism is observed near the Se K absorption edge in a monoclinic crystal of selenolanthionine monohydrate using linearly polarized synchrotron radiation and is explained by a simple molecular-orbital model. The complex anomalous-scattering tensor of selenium, measured by diffraction in a tetraronal crystal of the anhydrous compound, exhibits anisotropy nearly 6 for f' and 7 for f", the most yet found for a K edge. The crystal structure was determined for D-(-)-selenolanthionine, space group P4(3)2(1)2, a = 6.651 (2), c = 21.758 (5) A, Z = 4, R = 0.027 for 304 unique reflections.