Magnesium tungstate is an inorganic compound with the chemical formula MgWO4. It is a white, water-insoluble solid that crystallizes in the wolframite structure. It occurs naturally as the rare mineral huanzalaite.
Occurrence Magnesium tungstate occurs naturally as huanzalaite, MgWO4, a rare member of the wolframite group.
Preparation Magnesium tungstate can be prepared by solid-state reaction of magnesium oxide with tungsten trioxide:
MgO + WO3 → MgWO4
It can also be precipitated from aqueous solutions of a magnesium salt and sodium tungstate. For example:
Mg(NO3)2 + Na2WO4 → MgWO4↓ + 2 NaNO3
Structure and properties Magnesium tungstate crystallizes in the monoclinic crystal system with the wolframite-type structure, in space group P2/c (No. 13). The structure consists of distorted MgO6 and WO6 octahedra arranged in chains.
A high-temperature polymorph is reported above about 1065 °C.
Hydrated forms are also known. The dihydrate, MgWO4·2H2O, crystallizes in space group P21/c and dehydrates topotactically on heating to give anhydrous MgWO4.
A monohydrate, MgWO4·H2O, has also been prepared and structurally characterized.
At high pressure, MgWO4 undergoes structural changes similar to those observed in related wolframite-type tungstates.
Applications Magnesium tungstate is a luminescent material and has been used and investigated as a phosphor. Its emission is associated primarily with electronic transitions involving the tungstate groups.
MgWO4 has also been investigated as a scintillating material and as a host lattice for luminescent dopants.
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