Octamolybdate ion

The octamolybdate ion. Salts with the ratio M0O3 M2O equal to 4 1 have been called tetramolybdates. An X-ray study of the ammonium salt showed that it contains ions MogO illustrated in Fig. 11.4(c) and (d) it should therefore be formulated (NH4)4Mog026- 5 H2O. In this ion six of the MoOg octahedra are arranged in the same way as in the M07O24 ion, as shown in Fig. 11.4(b). 

The structures of both the heptamolybdate and octamolybdate ions in crystals are discussed on page 954 in relation to other heteropoly and isopoly anion structures. 

Mo20 24 2h), and octamolybdate, MogO g) ions. Even larger aggregates may be present in solution and in salts. Both and... 

Numerous investigations have shown the existence of the heptamolybdate, [Mo7024]6 , and octamolybdate, [Mo8026]4, ions in aqueous solution. Potentiometric measurements with computer treatment of the data proved to be one of the best methods to obtain information about these equilibria. Stability constants are calculated for all species in a particular reaction model, which is supposed to give the best fit between calculated and experimental points. In the calculations the species are identified in terms of their stoichiometric coefficients as described by the following general equation for the various equilibria... 

Ammonium ion forms several isopolymolybdates, including ammonium di-, tri-, hepta-, and octamolybdates. Among these, ammonium dimolyhdate, (NH4)2Mo20y [27546-07-2] and ammonium heptamolyhdate,... 

Fig. 32. Peak shapes, calculated from crystal structure parameters for the heptamo-lybdate ion, Mo70246", and for two octamolybdates Mo80264 and Mo80288". The separate contributions from Mo—Mo distances (short dashes), Mo—0 distances (dotted lines), and O—0 distances (long dashes) are shown.

Tetramolybdates or metamolybdates, M20-4Mo03- H20, are formed from concentrated solutions of alkali molybdates treated with 1.5 mols per mol of hydrochloric acid. Octamolybdates are obtained similarly from solutions containing 1.75 mols per mol of hydrochloric acid or by adding the calculated amount of M0O3 to ammonium paramolybdate solution. Both the tetra- and octa-molybdates are derived from the ion [Mo8026]4. ... 

Fig. 26-C-2. (a) Diagrammatic representation of Mo06 and W06 octahedra used in showing structures of some isopoly and heteropoly anions, (b) The structure of the para-molybdate anion, [M07O24]6". (c) The structure of the octamolybdate anion, [Moa026l4 (note that one Mo06 octahedron is completely hidden by the seven that are shown), (d) The structure of the [W12C>4.2]12- unit in the paratungstate ion.

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