X-ray powder diffraction analysis of two new magnesium selenate hydrates, MgSeO4·9H2O and MgSeO4·11H2O. Issue 2 (8th May 2015)

• Record Type: Journal Article
• Authors: Fortes, A. Dominic
• Is Part Of: Powder diffraction. Volume 30:Issue 2(2015)
• Page Start: 149
• Page End: 157
• Publication Date: 2015-05-08
• Subjects: Powder metallurgy -- Periodicals; Materials -- Analysis -- Periodicals; 620.1127
• DOI: 10.1017/S0885715615000123
• Languages: English
• ISSNs: 0885-7156

Abstract

<abstract abstract-type="normal"> <title> <x content-type="archive" xml:space="preserve">Abstract</x> </title> <p>Several hitherto unknown hydrates of magnesium selenate have been formed by quenching aqueous solutions of MgSeO<sub>4</sub> in liquid nitrogen. MgSeO<sub>4</sub>·11H<sub>2</sub>O is apparently isostructural with the mineral meridianiite (MgSO<sub>4</sub>·11H<sub>2</sub>O), being triclinic, <inline-formula><alternatives><inline-graphic xlink:href="ark:/27927/pgj1cjs8rqw" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><tex-math><![CDATA[$P{\rm \bar 1}$]]></tex-math></alternatives></inline-formula>, <italic>Z</italic> = 2, with unit-cell parameters <italic>a</italic> = 6.779 00(8) Å, <italic>b</italic> = 6.965 16(9) Å, <italic>c</italic> = 17.4934(2) Å, <italic>α</italic> = 87.713(1)°, <italic>β</italic> = 89.222(1)°, <italic>γ =</italic> 63.121(1)°, and <italic>V</italic> = 736.15(1) Å<sup>3</sup> at −25 °C. MgSeO<sub>4</sub>·9H<sub>2</sub>O represents a new hydration state in the MgSeO<sub>4</sub>–H<sub>2</sub>O system; it is monoclinic, space-group <italic>P</italic>2<sub>1</sub><italic>/c</italic>, <italic>Z</italic> = 4, with unit-cell parameters <italic>a</italic> = 7.270 24(6) Å, <italic>b</italic> = 10.510 94(9) Å, <italic>c</italic> = 17.4030(2) Å, <italic>β</italic> = 109.447(1)°, and <italic>V</italic> = 1254.02(1) Å<sup>3</sup> at −22 °C. The heavy-atom structure of MgSeO<sub>4</sub>·9H<sub>2</sub>O has been determined by direct-space methods from X-ray powder diffraction data and consists of isolated Mg(H<sub>2</sub>O)<sub>6</sub><sup>2+</sup> octahedra and SeO<sub>4</sub><sup>2−</sup> tetrahedra linked by hydrogen bonds. The remaining three water molecules occupy the space between the polyhedral ions, contributing to the H-bonded network, which comprises 4-, 5-, and 6-membered rings. A third phase has been observed to crystallise prior to the 11-hydrate upon warming of liquid-nitrogen-quenched glass, but this transforms rapidly to the meridianiite-structured 11-hydrate and the identity of this phase is unclear.</p> </abstract>