Molybdenum and its applications
Molybdenum is a transition element. In the Periodic Table molybdenum is in Group 6, located vertically between chromium and tungsten and horizontally in the second transition series between niobium and technetium (Fig. 1).
In some respects molybdenum has a diagonal relationship with vanadium and rhenium. For example, in their highest oxidation states they form tetrahedral oxoanions, [VO4]3−, [MoO4]2−, and [ReO4] − ; rhenium occurs in molybdenum disulfide (molybdenite) ores.
Fig 1: Position of
molybdenum in the
Molybdenum is a metallic element. It is sometimes described as a 'heavy metal' although its properties are very different from the properties of the typical heavy metals, mercury, thallium and lead. For example, it is much less toxic than these and other heavy metals.
The outstanding feature of molybdenum is its chemical versatility:
- Oxidation states from (−II) to (VI)
- Coordination numbers from 4 to 8
- Varied stereochemistry
- The ability to form compounds with most inorganic and organic ligands, with a particular preference for oxygen, sulfur, fluorine and chlorine donor atoms
- Formation of bi- and polynuclear compounds containing bridging oxide, chloride ligands or molybdenum-molybdenum bonds
It is this versatility which makes the chemistry of molybdenum challenging and exciting, and the actual and potential applications of its compounds many and varied. Molybdenum is the first of the transition metals to have an extensive sulfur chemistry shown by:
- Having as its principal ore molybdenum disulfide, MoS2
- Its binding by sulfur ligands in molybdenum-containing enzymes
- Application of MoS2 as an important industrial catalyst
- Formation of many sulfur complexes some of which are used as soluble lubricating oil additives
Molybdenum-based technical chemicals exploit the versatility of molybdenum chemistry in oxidation states - (VI), (V) and (IV). Many of the properties of molybdenum provide development opportunities and new commercial applications through the exploitation of its chemistry.