An anion or polyatomic ion known as a polyoxometalate (abbreviated POM) is made up of three or more transition metal oxyanions that are connected by shared oxygen atoms to create closed three-dimensional frameworks. The metal atoms are often transition metals from groups 6 (Mo, W) or 5 (V, Nb, Ta) in their high oxidation states. The diamagnetic anions of polyoxometalates are frequently colourless, orange, or red. Isopolymetalates, which contain only one kind of metal and oxide, and heteropolymetalates, which include one metal, oxide, and a main group oxyanion, are two recognised wide families (phosphate, silicate, etc.). There are several exceptions to these generalisations. Commercial catalysts for the oxidation of organic compounds use POMs.