Molybdic acid refers to hydrated forms of

molybdenum trioxide Molybdenum trioxide describes a family of inorganic compounds with the formula MoO3(H2O)n where n = 0, 1, 2. The anhydrous compound is produced on the largest scale of any molybdenum compound since it is the main intermediate produced when molybd ...

and related species. The

monohydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

(MoO₃·H₂O) and the

dihydrate In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...

(MoO₃·2H₂O) are well characterized. They are yellow diamagnetic solids.

Structure of the solids

Solid forms of molybdic acid are

coordination polymer Coordination may refer to: * Coordination (linguistics), a compound grammatical construction * Coordination complex, consisting of a central atom or ion and a surrounding array of bound molecules or ions ** A chemical reaction to form a coordinat ...

s. The monohydrate MoO₃·H₂O consists of layers of octahedrally coordinated MoO₅·(H₂O) units where 4 vertices are shared.Wells A.F. (1984) ''Structural Inorganic Chemistry'' 5th edition Oxford Science Publications The dihydrate (image shown above) has the same layer structure with the "extra" H₂O molecule intercalated between the layers.

Structure of molybdic acid in solution

In acidified aqueous solutions of molybdic acid, the complex is observed. Once again, molybdenum adopts

octahedral molecular geometry In chemistry, octahedral molecular geometry, also called square bipyramidal, describes the shape of compounds with six atoms or groups of atoms or ligands symmetrically arranged around a central atom, defining the vertices of an octahedron. The o ...

, probably with three oxo ligands and three

aquo ligand In chemistry, metal aquo complexes are coordination compounds containing metal ions with only water as a ligand. These complexes are the predominant Chemical species, species in aqueous solutions of many metal Salt (chemistry), salts, such as meta ...

s.Solution structure of molybdic acid from Raman spectroscopy and DFT analysis, Oyerindea O.F., Week C.L., Anbarb A.D., Spiro T.G. Inorganica Chimica Acta, 361, 4, (2008), 1000-1007, The salts of molybdic acid are called

molybdate In chemistry, a molybdate is a compound containing an oxyanion with molybdenum in its highest oxidation state of +6: . Molybdenum can form a very large range of such oxyanions, which can be discrete structures or polymeric extended structures, ...

s. They arise by adding base to solutions of molybdic acid.

Applications

Many molybdenum oxides are used as

heterogeneous catalyst Heterogeneous catalysis is catalysis where the phase of catalysts differs from that of the reagents or products. The process contrasts with homogeneous catalysis where the reagents, products and catalyst exist in the same phase. Phase distingui ...

s, e.g. for

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

s. Molybdic acid and its salts are used to make the Froehde reagent for the presumptive identification of alkaloids.

References

{{Molybdenum compounds Transition metal oxoacids Molybdates Coordination polymers