issue contents
April 2013 issue

Cover illustration: The heavy-atom framework in MgSO4·11H2O (with H atoms omitted for clarity). Dashed and solid lines are used to distinguish the hydrogen-bonded rings in different planes. See Fortes, Wood & Gutmann [Acta Cryst. (2013), C69, 324-329].
editorial
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inorganic compounds
A sample of Li0.41(NH4)0.59ClO4 was prepared by gel diffusion using agar agar gel as the medium of growth at ambient temperature. The Cl and mixed Li/N atoms are located on special positions. The structure features a twofold interpenetrated three-dimensional entanglement architecture, in which single three-dimensional networks are constructed from tetrahedral coordination based on diamondoid arrays. The crystal structure is compared with those of related compounds.
Four clathrates with type-I and type-II structure are reported in the K–Ba–Ga–Sn system. For the type-I compound, all framework sites are occupied by a mixture of Ga and Sn atoms, with Ga showing a preference for Wyckoff site 6c. For the type-II structures, only the smaller (Ga,Sn)24 pentagonal dodecahedral cages are filled, while the (Ga,Sn)28 hexakaidecahedral cages remain empty.
The structure of magnesium sulfate undecahydrate and its hexavalent chromium-bearing analogue are compared, elucidating details of the strain distribution through the hydrogen-bonded structure due to the substitution of a much larger oxyanion.
Analysis of the title compound, diiron(III) trisulfate–sulfuric acid–water (1/1/28), at 100 and 200 K reveals the structural features of an alum, (H5O2)Fe(SO4)2·12H2O. The Fe(H2O)6 unit is located on a centre of inversion, while the H5O2+ cation is located about an inversion centre. The compound thus represents the first oxonium alum, although the unit cell is orthorhombic.
The crystal structure of KAlSiO4-O1 was refined from single-crystal data, taking multiple twinning into account. Electron microprobe analysis confirmed that the compound is not stoichiometric.
metal-organic compounds
organic compounds
addenda and errata
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