Crystal structure of magnesium selenate heptahydrate, MgSeO47H2O, from neutron time-of-flight data

Abstract

MgSeO47H2O is isostructural with the analogous sulfate, MgSO47H2O, consisting of isolated [Mg(H2O)6]2+octahedra and [SeO4]2-tetrahedra, linked by O - O hydrogen bonds, with a single interstitial lattice water molecule. As in the sulfate, the [Mg(H2O)6]2+coordination octahedron is elongated along one axis due to the tetrahedral coordination of the two apical water molecules; these have Mg - O distances of ∼2.10 Å, whereas the remaining four trigonally coordinated water molecules have Mg - O distances of ∼2.05 Å. The mean Se - O bond length is 1.641 Å and is in excellent agreement with other selenates. The unit-cell volume of MgSeO47H2O at 10 K is 4.1% larger than that of the sulfate at 2 K, although this is not uniform; the greater part of the expansion is along the a axis of the crystal.