Scheelite, CaWO structures

The X-ray crystal structure of K[RuO ] shows the salt to have the scheelite (CaWO ) structure with a slightly flattened tetrahedral anion (mean Ru=(0) 1.79 A) [451], A single crystal X-ray structure of TRAP shows this to contain the expected tetrahedral anion [472],... 

Figure 2. A representation of the scheelite (CaWO ) structure. Reproduced by permission from Ann N. Y. Acad. Sci., Vol. 272, p 23, authors A Sleight and W. Linn.

The scheelite structure-type Is commonly adopted by compounds with the stoichiometry ABO, when the A cation Is fairly large (>1.0 A) and the B cation fairly small (on the order of 0.6 A). The prototype of this structure Is the mineral scheelite, CaWO, which crystalllzes( ) with four formula units... 

Figure 3. Ideal scheelite structure compared to ordered defect structures. Projection is down the c axis with only 1/2 the unit cell shown in this direction. Shaded circles and tetrahedra are at the top of level, unshaded 1/4 of the way down the unit cell, (a) CaWO. (b) La2 (Mo04)3. (c) Eu2(WO4)3. (d) Bi2(MoO4). ...

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