In chemistry, a heteropolymetalate is a subset of the polyoxometalates. They consist of three or more transition metal oxyanions linked together by shared oxygen atoms to form closed 3-dimensional molecular framework. In contrast to isopolymetalates, the heteropolymetallates contain main group oxy anions. The metal atoms are usually group 6 (Mo, W) or less commonly group 5 (V, Nb, Ta) transition metals in their highest oxidation states. They are usually colorless to orange, diamagnetic anions. For most heteropolymetalates the W, Mo, or V, is complemented by main group oxyanions phosphate and silicate. Many exceptions to these general statements exist, and the class of compounds includes hundreds of examples.