Chelated heteroatoms in polyoxometalates and the topological equivalence of {CoIII(en)} to type II cis-dioxometal centers. Synthesis and structure of [{Co(en)((mu)-OH)2Co(en)}{PW10O37Co(en)}2]^8- and [K(subset){Co(en)WO4}{WO(H2O)}(PW9O34)2]^12-

The first examples of polyoxometalate structures that incorporate embedded chelated heteroatoms point to new possibilities for stereochemical control of applications.