Crystal Structure of 3MgO·2CO2 Solved by Monte Carlo Simulation

Abstract

The crystal structure of the intermediate phase (3MgO·2CO 2 ) of synthetic nesquehonite (MgO·3H 2 O) following heat treatment was solved by Monte Carlo simulation using powder X-ray diffraction data and was confirmed by Rietveld refinement. The phase is cubic with space group I43m and cell constants of a = 8.516(13)Å. The unit cell consists of independent atoms such as magnesium, carbon, and two oxygen atoms. The magnesium atom is surrounded by six oxygen atoms in octahedral coordination, and four symmetrically identical MgO 6 octahedra in a edge-sharing arrangement form an Mg 4 O 17 block in the (100) planes of a unit cell. These Mg 4 O 17 blocks share edges with other Mg 4 O 17 blocks to form a framework structure. A CO 3 triangle that exists on the three-fold axis connects three Mg 4 O 17 blocks.

Synthesis, electron microscopy and X-ray characterization of oxymagnesite, MgO·2MgCO3, formed from amorphous magnesium carbonate

“…The structure, with the space group I4 ¯3m, a = 8.5205(1) nm and the atomic parameters listed in Table 2, refined from the diffractogram (see Fig. 7) matches the structure reported by Watabe et al 7 well, except for the fact that the (2 2 0) peak almost disappears during the refinement which is assumed to be due to the low occupancy of the O atom at the 8c site stipulated in this previous work. Instead the occupancies of both O-atom sites were refined resulting in partial occupation of both positions, both about 90% filled.…”

“…2 and 7. The full pattern refinement of the powder X-ray diffractogram of sample E shows a good fit to the structure reported by Watabe et al 7 except for the O-atom occupancies (see Fig. 7).…”

“…Oxymagnesite is a peculiar compound that has only been described in a few previous studies most often formed from thermal decomposition of various hydrated magnesium carbonates such as nesquehonite. [5][6][7] In the decomposition reaction the formation of oxymagnesite has been attributed to the non-equivalent positions of the CO 3 groups in the nesquehonite crystal which allows one third of the CO 3 2− anions to lose CO 2 upon thermal treatment at a lower temperature compared to the remaining CO 3 groups. 6 Oxymagnesite has also been reported to form from a reaction between Mg(OH) 2 and CO 2 in an anhydrous synthesis 8 and from a solid state reaction of CO 2 and MgO using steam.…”

Assembly of Lyotropic Liquid Crystals with Solid Crystal’s Structural Order Translated from the Lipid Rafts in Cell Membranes

“…For example, the XRD pattern of 3MgO•2CO 2 solid crystal with I4̅ 3m space group shows 21 peaks. 24 θ. With its d 100 = 31.100 Å, 7 diffraction peaks are predicted in this range, and all of them are clearly observed and regularly spaced despite the fact that this pattern is recorded using conventional X-ray radiation.…”

“…The overall pattern, the number of peaks, and their intensities are comparable with those of cubic solid crystals. For example, the XRD pattern of 3MgO·2CO 2 solid crystal with I 4̅3 m space group shows 21 peaks Figure (d–f) shows lamellar liquid crystals.…”