In chemistry, a molybdate is a compound containing an oxoanion with molybdenum in its highest oxidation state of 6: O−−Mo(=O)2−O−. 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 MoO2−4, found in potassium 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, CrO2−4, Cr2O2−7, Cr3O2−10 and Cr4O2−13 ions which are all based on tetrahedral chromium. Tungsten is similar to molybdenum and forms many tungstates containing 6 coordinate tungsten.