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In comparison with the previous structure determination of the β-modification of barium catena-polyphosphate that was based on Weissenberg film data [Grenier et al. (1967). Bull. Soc. Fr. Minéral. Cristallogr. 90, 24–31], the current CCD-data-based redetermination reveals all atoms with anisotropic displacement parameters, standard uncertainties for the atomic coordinates, and the determination of the absolute structure. Moreover, a much higher accuracy in terms of the bond-length distribution for the polyphosphate chain, with two shorter and two longer P—O distances, was achieved. The structure consists of polyphosphate chains extending parallel to [100] with a periodicity of two PO4 tetra­hedra. The Ba2+ cations are located between the chains and are surrounded by ten O atoms in the form of a distorted coordination polyhedron, with Ba—O distances ranging from 2.765 (3) to 3.143 (3) Å, also reflecting the higher precision of the current redetermination.

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The basic building units of the hydrous periodate Pb3(IO4(OH)2)2 are three Pb2+ cations and two IO4(OH)23− anions. The octa­hedral anions are arranged in a distorted hexa­gonal rod packing, with the cations (each with a coordination number of eight) located in between.

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2,5-Di­azido-1,4-phenyl­ene di­acetate and dibutyrate are the first structurally characterized representatives with a trans-di­azido­phenyl­ene entity. Both mol­ecules possess inversion symmetry; however, the compounds crystallize in different crystal systems (triclinic versus monoclinic).

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The crystal structure of [NiHg(SCN)4(CH3OH)2]n is made up of HgS4 tetra­hedra and trans-NiN4O2 octa­hedra, linked together by thio­cyanato bridges. The methanol mol­ecules point to the cavities of the resulting framework.

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The crystal structures of the 1.5- and 10-hydrates of Na2SeO4 are isotypic with those of the corresponding chromates.

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The mol­ecular structure of the title compound is centrosymmetric. The cyclo­hexa-2,5-diene moiety is exactly planar and has a bond-length distribution characteristic for one pair of double bonds and two pairs of single bonds.
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