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ISSN: 2053-2296

Polymorphism special issue (December 2011)

Guest Editor(s): A. Linden

Polymorphism, particularly for molecular materials, was perhaps once considered a curiosity. Nowadays, polymorphism has become a crucial issue for the pharmaceutical industry. Different polymorphs of a drug can have quite different properties in terms of solubility, bioavailability, shelf life, ease of production, and other physical properties. Developments in crystal structure prediction in recent years have also highlighted hitherto unknown polymorphs.

Highlighted illustration

Cover illustration: Differences in stacking for polymorphs of aspirin viewed down the b axis [Chan, Welberry, Heerdegen & Goossens (2010). Acta Cryst. B66, 696-707].

Acta Cryst. (2011). C67, e15
doi: 10.1107/S0108270111046968

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The title structure is a new modification of Tl2CrO4. It is closely related to the already known modification which belongs to the β-K2SO4 family, but it differs in the number of independent cations and anions: there are four independent Tl+ cations and two [CrO4]2− anions in the title structure, in contrast with the β-K2SO4 family where there are two independent cations and one anion.

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The Cu2Se3Sn structure investigated in this paper is a superstructure of the cubic and monoclinic modifications reported earlier. The eight independent Cu atoms and four independent Sn atoms occupy, respectively, one-third and one-sixth of the tetra­hedral holes in a pseudo-close-packed Se lattice. The cation positions are fully ordered.

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The title compound contains infinite chains built up from V(H2O)2O4 octa­hedra and SeO3 pyramids. A network of O—H⋯O hydrogen bonds helps to consolidate the packing.

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β-Zn3(AsO3)2 contains unusual edge-sharing ZnO4 tetra­hedra as part of its three-dimensional array of ZnO4 and AsO3 units. It is a polymorph of the mineral reinerite, which also contains edge-shared ZnO4 tetra­hedra.

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The structural transition in SrV6O11 was studied in detail by single-crystal X-ray diffraction and specific heat measurements. The specific heat showed three anomalies at 43.8, 77.7 and 322 K. The diffraction study established that SrV6O11 crystallizes in P63mc at 353 K, but in P63/mmc at room temperature. The present study establishes that the P63/mmc to P63mc transition takes place at 322 K, coinciding with the magnetic transition.

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A new ferric sulfate trihydrate has been synthesized at 403 K under hydro­thermal conditions. The structure consists of quadruple chains of [Fe2(SO4)3(H2O)3]^0_{\infty} parallel to [010]. Each quadruple chain is composed of equal proportions of FeO4(H2O)2 octa­hedra and FeO5(H2O) octa­hedra sharing corners with SO4 tetra­hedra. The chains are joined to each other by hydrogen bonds.

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The structure of the rhombohedral form of EuNi5In consists of CaCu5 (EuNi5)-, MgCu2 (InNi2)- and NiAs (EuNi)-type slabs in a 1:2:1 ratio. The structure features a two-dimensional network of 2[Ni8] tetra­hedral clusters arranged in the ab plane.

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The single crystals of the tetra­gonal modification of dysprosium orthomolybdate obtained in the present work are stable at room temperature. The crystal structure is formed by corner-sharing MoO4 tetra­hedra and Dy polyhedra coordinated by seven O atoms.

Special and virtual issues

Acta Crystallographica Section C is planning special issues on

The Structural Chemistry of Homogeneous and Heterogeneous Catalysts

NMR Crystallography

Full details are available on the special issues page.

The latest virtual issue, featuring Coordination polymers and with an introduction by Len Barbour, was published in July 2014.

What are the 'most read' articles from the recent special issues?

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