Crystal structure of magnesium selenate hepta­hydrate, MgSeO(4)·7H(2)O, from neutron time-of-flight data

MgSeO(4)·7H(2)O is isostructural with the analogous sulfate, MgSO(4)·7H(2)O, consisting of isolated [Mg(H(2)O)(6)](2+) octa­hedra and [SeO(4)](2−) tetra­hedra, linked by O—H⋯O hydrogen bonds, with a single inter­stitial lattice water mol­ecule. As in the sulfate, the [Mg(H(2)O)(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 MgSeO(4)·7H(2)O 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.