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(NH 4 )Mg(HSO 4 )(SO 4 )(H 2 O) 2 and NaSc(CrO 4 ) 2 (H 2 O) 2 , two crystal structures comprising kröhnkite‐type chains, and the temperature‐induced phase transition (NH 4 )Mg(HSO 4 )(SO 4 )(H 2 O) 2 (NH 4 )MgH(SO 4 ) 2 (H 2 O) 2
Author(s) -
Weil Matthias,
Kolitsch Uwe
Publication year - 2021
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 17
ISSN - 2053-2296
DOI - 10.1107/s2053229621001650
Subject(s) - triclinic crystal system , crystallography , octahedron , crystal structure , chemistry , hydrogen bond , tellurate , molecule , ion , organic chemistry
The crystal structure of the mineral kröhnkite, Na 2 Cu(SO 4 ) 2 (H 2 O) 2 , contains infinite chains composed of [CuO 4 (OH 2 ) 2 ] octahedra corner‐linked with SO 4 tetrahedra. Such or similar tetrahedral–octahedral `kröhnkite‐type' chains are present in the crystal structures of numerous compounds with the composition A n M ( X O 4 ) 2 (H 2 O) 2 . The title compounds, (NH 4 )Mg(HSO 4 )(SO 4 )(H 2 O) 2 , ammonium magnesium hydrogen sulfate sulfate dihydrate, and NaSc(CrO 4 ) 2 (H 2 O) 2 , sodium scandium bis(chromate) dihydrate, are members of the large family with such kröhnkite‐type chains. At 100 K, (NH 4 )Mg(HSO 4 )(SO 4 )(H 2 O) 2 has an unprecedented triclinic crystal structure and contains [MgO 4 (OH 2 ) 2 ] octahedra linked by SO 3 (OH) and SO 4 tetrahedra into chains extending parallel to [10]. Adjacent chains are linked by very strong hydrogen bonds between SO 3 (OH) and SO 4 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 three‐dimensional network. (NH 4 )Mg(HSO 4 )(SO 4 )(H 2 O) 2 shows a reversible phase transition and crystallizes at room temperature in structure type E in the classification scheme for structures with kröhnkite‐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(CrO 4 ) 2 (H 2 O) 2 adopts structure type F1 in the classification scheme for structures with kröhnkite‐type chains. Here, [ScO 4 (OH 2 ) 2 ] octahedra (point group symmetry ) are linked by CrO 4 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(CrO 4 ) 2 (H 2 O) 2 and its isotypic Na M (CrO 4 ) 2 (H 2 O) 2 ( M = Al and Fe) analogues.