(NH4)Mg(HSO4)(SO4)(H2O)2 and NaSc(CrO4)2(H2O)2, two crystal structures comprising kröhnkite-type chains, and the temperature-induced phase transition (NH4)Mg(HSO4)(SO4)(H2O)2 ⇔ (NH4)MgH(SO4)2(H2O)2

Author(s): Matthias Weil, Uwe Kolitsch
Abstract: The crystal structure of the mineral kro hnkite, Na2Cu( SO4)2(H2O)(2), contains infinite chains composed of [CuO4(OH2)(2)] octahedra corner-linked with SO4 tetrahedra. Such or similar tetrahedral-octahedral 'krohnkite-type' chains are present in the crystal structures of numerous compounds with the composition AnM(XO4)(2)(H2O)(2). The title compounds, (NH4)Mg(HSO4)(SO4)(H2O)(2), ammonium magnesium hydrogen sulfate sulfate dihydrate, and NaSc(CrO4)(2)(H2O)2, sodium scandium bis(chromate) dihydrate, are members of the large family with such kro hnkite-type chains. At 100 K, (NH4)Mg(HSO4)(SO4)(H2O) 2 has an unprecedented triclinic crystal structure and contains [MgO4(OH2)(2)] octahedra linked by SO3(OH) and SO4 tetrahedra into chains extending parallel to [110]. Adjacent chains are linked by very strong hydrogen bonds between SO3(OH) and SO4 tetrahedra into layers parallel to (111). Ammonium cations and water molecules connect adjacent layers through hydrogen-bonding interactions of medium-to-weak strength into a threedimensional network. (NH4)Mg(HSO4)(SO4)(H2O) 2 shows a reversible phase transition and crystallizes at room temperature in structure type E in the classification scheme for structures with kro hnkite-type chains, with half of the unit-cell volume for the resulting triclinic cell, and with disordered H atoms of the ammonium tetrahedron and the H atom between two symmetry-related sulfate groups. IR spectroscopic room-temperature data for the latter phase are provided. Monoclinic NaSc(CrO4)(2)(O-H2)(2) adopts structure type F1 in the classification scheme for structures with kro hnkite-type chains. Here, [ScO4(OH2)(2)] octahedra (point group symmetry 1) are linked by CrO4 tetrahedra into chains parallel to [010]. The Na+ cations (site symmetry 2) have a [6 + 2] coordination and connect adjacent chains into a three-dimensional framework that is consolidated by medium-strong hydrogen bonds involving the water molecules. Quantitative structural comparisons are made between NaSc(CrO4)2(H2O)(2) and its isotypic NaM(CrO4)(2)(H2O)(2) (M = Al and Fe) analogues.
Organisation(s): Department of Mineralogy and Crystallography
External organisation(s): Naturhistorisches Museum Wien (NHM), Technische Universität Wien
Journal: Acta Crystallographica. Section C: Structural Chemistry
Volume: C77
Pages: 144-151
No. of pages: 8
ISSN: 2053-2296
DOI: https://doi.org/10.1107/S2053229621001650
Publication date: 03-2021
Peer reviewed: Yes
Austrian Fields of Science 2012: 104026 Spectroscopy, 104011 Materials chemistry, 105113 Crystallography
Keywords
ASJC Scopus subject areas: Condensed Matter Physics, Materials Chemistry, Inorganic Chemistry, Physical and Theoretical Chemistry
Portal url: https://ucrisportal.univie.ac.at/en/publications/288e7e05-e3fe-4b41-9b10-61dd9ee4b21f

Back