Cover illustration: A view of the three-dimensional hydrogen-bonded pts framework in 4,4'-bi(1H-pyrazol-2-ium) tetrachloridoaurate(III) chloride, down the c axis, showing how the tetrachloridoaurate(III) stacks are incorporated inside the channels. N atoms are shaded and dotted lines indicate hydrogen bonding. See Domasevitch [Acta Cryst. (2012), C68, m169-m172].
X-ray diffraction reveals a new polymorph of volborthite in a single crystal prepared by hydrothermal means. The structure is monoclinic (space group C2/c) at room temperature, with the unit cell doubled with respect to the previously reported C2/m structure.
In the title compound, each singly protonated diphosphopentamolybdate(VI) anion retains the typical geometry of a ring of five edge-sharing MoO6 octahedra, except for one corner-sharing link. Two capping PO4 tetrahedra share corners with the five octahedra. Despite being surrounded by an extensive network of hydrogen bonds, predominantly from the guanidinium cations, short P—O—H⋯O=P contacts associate the anions into infinite columns generated by the c-glide.
The title compound, Li0.97FeII0.79FeIII0.15(PO4), has been synthesized hydrothermally at 973 K and 0.1 GPa. Its crystal structure is similar to that of natural triphylite and is characterized by two chains of edge-sharing octahedra parallel to the b axis. The M1 octahedra contain Li and vacancies, and the M2 octahedra contain FeII, FeIII and vacancies.