1. Isopolymolybdates Heteropolytungstates Formation and Structure

2. Examples V 10 O 28 2- Mo 7 O 24 6- Mo 8 O 26 4-Ta 6 O 19 8- Al 13 O 4 (OH) 24 (H 2 O) 12 7+ or AlO 4 Al 12 (OH) 24 (H 2 O) 12 7+ PW 12 O 40 3- P 2 W 18 O 62 6- Co 4 P 4 W 30 O 112 (H 2 O) 2 16- or Co 4 (H 2 O) 2 (P 2 W 15 O 56 ) 2 16- As 12 Ln 16 (H 2 O) 36 W 148 O 524 76-

3. ? ? ? How do we make sense of these?

4. Chromate - Dichromate CrO 4 2- + 2 H + → Cr 2 O 7 2- + H 2 O yellow orange Think of CrO 4 2- as being composed of 4 O 2- with a central Cr 6+ One O 2- is neutralized by the acid. O 2- + 2 H + → H 2 O

5. Chromate - Dichromate The Cr 2 O 7 2- ion has each Cr at the center of a tetrahedron with the two tetrahedrons sharing a corner.

6. Chromate ion Dichromate ion

7. Molybdates Molybdates form polyions by edge sharing rather than corner sharing. The Mo 6+ ions are at the center of an octahedron.

8. Polymolybdates Unlike chromates. MoO 4 2- → Mo 7 O 24 6- → Mo 8 O 26 4- → Mo 36 O 112 8-

9. Molybdates and Tungstates What three structures can be built from three octahedrons by edge sharing? No corner sharing. No face sharing.

10. 1 1

11. 2 2

12. 3 3

13. 3 From Opposite Side 3

14. What’s in the Literature? Lots of errors in the older literature. Systems not at equilibrium when measured, especially tungsten systems. Bad theory. Assumed that diffusion in solution was only related to molecular weight (like gases).

15. Isopolymolybdates Maximize 60°; minimize others

16. Keggin Structure When structures get large, must have some corner sharing.

17. A Heteropolytungstate: W 12 O 40 8-

18. Another View

19. Synthesis Product depends on: stoichiometry of reactants pH temperature A variety of ions can be put into the cavity. P(V), Si(IV), Co(II), Co(III), C(IV),...

20. Synthesis Can also have a heteroion replace one of the tungstens. A P(V) in the center and a Co(II) replacing a W. A Co(II) in the center and a Co(II) replacing a W.

21. Synthesis Co 2+ + WO 4 2- → CoW 11 Co(H 2 O)O 39 8- precipitate potassium salt CoW 11 Co(H 2 O)O 39 8- + H + → CoW 12 O 40 6- (aq) this contains Co 2+ in the center Oxidize to Co 3+ → CoW 12 O 40 5- precipitate as potassium salt Result: tetrahedral Co(III) in the center

22. Lacunary Structures Can have structures with a piece of the regular structure missing. Remove a W 3 unit from the Keggin structure and have a W 9 structure remaining. Put two of those W 9 structures together and get the Dawson structure.

23. Dawson Structure P 2 W 18 O 62 6-

24. The Compound with Four Cobalts Co 4 (H 2 O) 2 (P 2 W 15 O 56 ) 2 16-

25. M(H 2 O)P 5 W 30 O 110 14- The Lemon Green: metal ionBlue: water Red: phosphorus

26. As 12 Ln 16 (H 2 O) 36 W 148 O 524 76-