In chemistry a molybdate is a compound containing an oxoanion with molybdenum in its highest oxidation state of 6. Molybdenum can form a very large range of such oxoanions which can be discrete structures or polymeric extended structures, although the latter are only found in the solid state.The larger oxoanions are members of group of compounds termed polyoxometalates, and because they contain only one type of metal atom are often called isopolymetalates[1]. The discrete molybdenum oxoanions range in size from the simplest MoO42-, found in sodium molybdate up to extremely large structures found in isopoly-molybdenum blues that contain for example 154 Mo atoms. The behaviour of molybdenum is different from the other elements in group 6. Chromium only forms the chromates, CrO42-, Cr2O72-, Cr3O102- and Cr4O132- ions which are all based on tetrahedral chromium. Tungsten is similar to molybdenum and forms many tungstates containing 6 coordinate tungsten[2].
Molybdic acid refers to hydrated forms of molybdenum trioxide.
The simplest form, the monohydrate, is MoO3.H2O, the dihydrate MoO3.2H2O is also known. The solid state structure of MoO3.H2O consists of layers of octahedrally coordinated MoO5(H2O) units where 4 vertices are shared.[1] the dihydrate has the same layer structure with the extra H2O molecule intercalated between the layers.
Molybdenite ore is processed by flotation to give relatively pure MoS2, the main contaminant being carbon. MoS2 also arises by the thermal treatment of virtually all molybdenum compounds with hydrogen sulfide.
In MoS2, each Mo(IV) center is trigonal prismatic, being bound to six sulfide ligands, each of which is pyramidal. The trigonal prisms are interconnected to give a layered structure, wherein molybdenum atoms are sandwiched between layers of sulfur atoms.
MoS2 with particle sizes in the range of 1-100 µm is a common dry lubricant. Few alternatives exist that can confer the high lubricity and stability up to 350 °C in oxidizing environments. Sliding friction tests of MoS2 using a pin on disc tester at low loads (0.1-2 N) give friction coefficient values of <0.1.
Molybdenum disulfide is the inorganic compound with the formula MoS2. This black crystalline sulfide of molybdenum occurs as the mineral molybdenite. More so than other transition metal chalcogenides, MoS2 is unreactive, being unaffected by dilute acids. In terms of its appearance and feel, molybdenum disulfide is similar to graphite and indeed it is widely used as a solid lubricant[1][2] due to its low friction properties, sometimes to relatively high temperatures.
Phosphomolybdic acid, also known as dodeca molybdophosphoric acid or PMA is a component of Masson's trichrome stain. It is a yellow-green compound, freely soluble in water and polar organic solvents such as ethanol. It is used as a reagent in thin layer chromatography for staining phenolics, hydrocarbon waxes, alkaloids and steroids.
Ammonium molybdate is an odourless crystalline compound ranging in colour from white to yellow-green. Its chemical formula is as follows; (nh4)6mo7o24. 4h2o.
It is also called molybdic acid hexammonium salt tetrahydrate, ammonium molybdate tetrahydrate, and ammonium heptamolybdate tetrahydrate.
Sodium molybdate, Na2MoO4, is useful as a source of molybdenum.[citation needed] It is often found as the dihydrate, Na2MoO4·2H2O.
The molybdate(IV) anion is tetrahedral. Two sodium cations coordinate with every one anion.[1]
| Specification | | Typical | |
| ------------ | | ------- |
| Assay (K2MoO4) | 99.5% min | | 99.70% |
| | | |
| Insoluble Matter | 0.01% max | | 99.70% |
| | | |
| Sulfate | 0.05% max | | <0.05% |
| | | |
| Chloride | 0.05% max | | <0.05% |
| | | |
| Phosphate | 0.03% max | | <0.03% |
| | | |
| Iron (Fe) | 0.01% max | | <0.01% |
| | | |
| Silicate (SiO2) | 0.01% max | | <0.01% |
| | | |
| Sodium (Na) | 0.25% max | | <0.10% |
