Cover illustration: The molecular structure of the [Cr(CO)5]2- anion in [2,2,2-crypt-K]2[Cr(CO)5] ethylenediamine monosolvate, with displacement ellipsoids drawn at the 30% probability level. See Zhai & Xu [Acta Cryst. (2011), C67, m202-m204].
The previously unknown crystal structure of magnesium perchlorate anhydrate, determined and refined from laboratory X-ray powder diffraction data, represents a new structure type. The structure consists of a three-dimensional network resulting from the corner-sharing of MgO6 octahedra and ClO4 tetrahedra.