Redetermination of K2Mg3(OH)2(SO4)3(H2O)2 from single-crystal X-ray data revealing the correct hydrogen-atom positions.

Matthias Weil

doi:10.1107/s2056989020016217

Abstract

In comparison with the previous structure determination of K2Mg3(OH)2(SO4)3(H2O)2, dipotassium trimagnesium di-hydroxide tris-(sulfate) dihydrate, from laboratory powder X-ray diffraction data [Kubel & Cabaret-Lampin (2013 ▸). Z. Anorg. Allg. Chem. 639, 1782-1786], the present redetermination against CCD single-crystal data has allowed for the modelling of all non-H atoms with anisotropic displacement parameters. As well as higher accuracy and precision in terms of bond lengths and angles, the clear localization of the H-atom positions leads also to a reasonable hydrogen-bonding scheme for this hy-droxy hydrate. The structure consists of (100) sheets composed of corner- and edge-sharing [MgO6] octa-hedra and sulfate tetra-hedra. Adjacent sheets are linked by the potassium cations and a hydrogen bond of medium strength involving the water mol-ecule. The title compound is isotypic with its CoII and MnII analogues: the three K2 M 3(OH)2(SO4)3(H2O)2 (M = Mg, Co, Mn) structures are qu-anti-tatively compared.

Highlights

In our recent projects focused on hydrothermal phaseformation studies in the systems M/XVI/TeIV/O/H (X = S, Se), it was tested whether tetrahedral sulfate or selenate anions can be incorporated into oxidotellurates(IV) of different divalent metals M
To the actual hydroxide O atom (O8); the second hydroxyl group (O9) shows a too large O—H distance accompanied with large DÁ Á ÁA distances or a too small O9—H2Á Á ÁO8 angle; the water molecule (O10) shows likewise either unreasonable HÁ Á ÁA distances or D—HÁ Á ÁA angles
Mg1 is bonded to four O atoms belonging to

Summary

Chemical context

In our recent projects focused on hydrothermal phaseformation studies in the systems M/XVI/TeIV/O/H (X = S, Se), it was tested whether tetrahedral sulfate or selenate anions can be incorporated into oxidotellurates(IV) of different divalent metals M. This concept proved to be successful for M = Hg (Weil & Shirkhanlou, 2015), M = Ca, Cd, Sr (Weil & Shirkhanlou, 2017a), M = Pb (Weil & Shirkhanlou, 2017b) as well as for M = Zn, Mg (Weil & Shirkhanlou, 2017c). A redetermination of the crystal structure of K2Mg3(OH)2(SO4)3(H2O) to establish a more reasonable hydrogen-bonding pattern by using single crystal X-ray diffraction CCD data seemed appropriate and is reported here

Structural commentary

Refinement