MgSO₄·11H₂O and MgCrO₄·11H₂O based on time-of-flight neutron single-crystal Laue data

Abstract

Hexaaquamagnesium(II) sulfate pentahydrate, [Mg(H2O)6]SO4·5H2O, and hexaaquamagnesium(II) chromate(II) pentahydrate, [Mg(H2O)6][CrO4]·5H2O, are isomorphous, being composed of hexaaquamagnesium(II) octahedra, [Mg(H2O)6](2+), and sulfate (chromate) tetrahedral oxyanions, SO4(2-) (CrO4(2-)), linked by hydrogen bonds. There are two symmetry-inequivalent centrosymmetric octahedra: M1 at (0, 0, 0) donates hydrogen bonds directly to the tetrahedral oxyanion, T1, at (0.405, 0.320, 0.201), whereas the M2 octahedron at (0, 0, ½) is linked to the oxyanion via five interstitial water molecules. Substitution of Cr(VI) for S(VI) leads to a substantial expansion of T1, since the Cr-O bond is approximately 12% longer than the S-O bond. This expansion is propagated through the hydrogen-bonded framework to produce a 3.3% increase in unit-cell volume; the greatest part of this chemically induced strain is manifested along the b* direction. The hydrogen bonds in the chromate compound mitigate ~20% of the expected strain due to the larger oxyanion, becoming shorter (i.e. stronger) and more linear than in the sulfate analogue. The bifurcated hydrogen bond donated by one of the interstitial water molecules is significantly more symmetrical in the chromate analogue.

Glycine zinc sulfate pentahydrate: redetermination at 10 K from time-of-flight neutron Laue diffraction

“…The coordinates of hydrogen atoms in this work were unrestrained and allowed to refine anisotropically.Our values for the N-H and C-H bond lengths are in excellent agreement with other single-crystal neutron diffraction work, as noted in the preceding paragraph. Our values for the O-H bond lengths also agree well with those found in similar environments in hydrated M(II) coordination compounds, such as MgSO 4 Á11H 2 O and MgCrO 4 Á11H 2 O where the average O-H = 0.974 Å(Fortes et al, 2013), MgSeO 4 Á9H 2 O, O-H av = 0.972 Å(Fortes et al, 2015), and MgSeO 4 Á7H 2 O, O-H av = 0.974 Å(Fortes & Gutmann, 2014).…”

Crystal structure of magnesium selenate heptahydrate, MgSeO4·7H2O, from neutron time-of-flight data

“…As part of a wider study into low-temperature crystal hydrates of MgSeO 4 and related compounds (Fortes et al, 2013) we synthesised the title compound and carried out a single-crystal neutron diffraction experiment in order to determine its structure.…”

X-ray powder diffraction analysis of two new magnesium selenate hydrates, MgSeO4·9H2O and MgSeO4·11H2O

“…In a series of papers, my colleagues and I reported the results of work to form structural analogues of MgSO 4 •11H 2 O in which the cation was replaced by Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ or Zn 2+ (Fortes et al, 2012a(Fortes et al, , 2012b and the oxyanion was replaced by CrO 4 2− : Fortes et al, 2013.…”

“…In a series of papers, my colleagues and I reported the results of work to form structural analogues of MgSO 4 •11H 2 O in which the cation was replaced by Mn 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ or Zn 2+ (Fortes et al, 2012a(Fortes et al, , 2012b and the oxyanion was replaced by CrO 4 2− (Fortes and Wood, 2012;Fortes et al, 2013). These efforts provide information on the response of the structure to chemically induced "internal" stress that are complementary to other means of generating strain in the crystal, such as variable temperature and pressure (cf., Fortes et al, 2008Fortes et al, , 2009Fortes et al, , 2012c.…”