Preparation, crystal structure, and luminescence of magnesium molybdate and tungstate monohydrates, MgMoO4 · H2O and MgWO4 · H2O

Triclinic MgMoO4 · H2O and the isomorphous MgWO4 · H2O have been prepared under mild hydrothermal conditions in single crystalline form and the crystal structure of MgMoO4 · H2O has been determined by X-ray diffraction. The structure is compared to a model deduced earlier for MgWO4 · H2O from topotaxy data, with which the general topology agrees, but there is an important difference in the orientation of MoO4-tetrahedra. The X-ray powder diffraction data, thermal dehydration behavior, as well as the luminescence properties are reported and the latter compared with data of related phases. Crystal data are: Triclinic, space group P −1; MgMoO4 · H2O: a = 5.665, Å, b = 5.869, Å, c = 6.875, Å, α = 100.80°, β = 95.05°, γ = 106.57°; MgWO4 · H2O: a = 5.681, Å, b = 5.887, Å, c = 6.870, Å, α = 100.85°, β = 95.44°, γ = 106.55°.