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