Redetermination of poly[μ-chlorido-hepta­chlorido-μ3-l-proline-μ2-l-proline-tetra­mercury(II)]

The asymmetric unit of the title compound, [Hg4Cl8(C5H9NO2)2]n, consists of four HgCl2 units and two L-proline ligands in the zwitterionic form. In each HgCl2 unit, the HgII ion is strongly bonded to two Cl atoms, and the HgII ions in two of the HgCl2 units are chelated by O atoms of two l-proline ligands, with one strong and one weak Hg—O bond. In the crystal structure, HgCl2 and L-proline units are linked to form an extended chain along the a axis. The chain structure is further stabilized by N—H⋯Cl hydrogen bonds, and the chains are arranged in layers parallel to the ab plane. The structure of the title compound was originally determined by Ehsan, Malik & Haider [(1996). J. Banglad. Acad. Sci. 20, 175] but no three-dimensional coordinates are available

Estimation of Single Crystal Integrated X-ray Intensity within a Designated (D?, D2?) Domain

It is shown that measurement of the integrated intensity of a Bragg X-ray reflection within a precisely defined area of the (Aw, A2() distribution (Mathieson 1982a) is possible using a standard scintillation detector. The method involves an aperture system in front of the detector, consisting of two halves which are independently controlled so that both the width and position of the aperture are variable and can follow the A2() boundaries of the sections of any specified convex domain in (Aw, A2() space, as the specimen crystal steps in Aw. By taking account of the dispersion of the wavelength, crystal mosaicity and source components, the method can (a) exclude those extraneous contributions which, particularly at low () angles, constitute a major error source with conventional fixed-aperture procedures and (b) obviate the so-called truncation error at high () angles. This boundary-following method therefore provides, by a simple instrumental operation, a much closer estimate of the true integrated intensity of a Bragg reflection from a small single crystal than is feasible with the use of a fixed aperture. Once the main parameters of the experiment are determined, the procedure requires no greater expenditure of time than the traditional fixed-aperture method.</jats:p

Small-crystal X-ray diffractometry with a crystal ante-monochromator: erratum

In the paper by Mathieson [Acta Cryst. (1985), A41, 309- 316] the definition of k given in the Abstract should read k = (Δλ/λ). </jats:p