Cover illustration: A view of part of the crystal structure of N,N-dimethylanilinium 3-cyano-4-(dicyanomethylene)-5-oxo-4,5-dihydro-1H-pyrrol-2-olate showing the formation via strong hydrogen bonds (N-HN and N-HO) of ribbons of anions and cations along the c axis. See Tafeenko, Peschar, Kaukova, Schenk & Aslanov [Acta Cryst. (2004), C60, o62-o64].
(NH4)4Cd(HSeIVO3)2(SeVIO4)2 contains kröhnkite-like chains in which CdO6 octahedra are linked via bridging HSeO3 groups. SeO4 groups, which decorate the chains, are attached to the CdO6 octahedra in a trans arrangement.
The title compound is isostructural with K2[FeF5(H2O)] and contains polymeric anion chains held together by strong O—H⋯F bonds. Each V atom is coordinated to five terminal F atoms and the O atom of one water molecule. Pairs of O—H⋯F bonds are formed by two cis-related F atoms. Twofold axes run along the O—V—F axis of the V-centred octahedra.