Understanding and mapping the assembly of a family of trimeric polyoxometalates: transition metal mediated Wells-Dawson (M18)-trimers

Four iso-structural triple Wells-Dawson-type phosphotungstate compounds incorporating six transition metal ion linkers are presented of the form [(M2P2W16O60)(3)](24-/30-), 1-4, where M = Co, Mn, Fe, Ni respectively and compounds 3 and 4 are revealed for the first time uniting a family of isostructural clusters. Further, a comparative study of the solid-state arrangements of polyoxoanions 1-4 is presented as well as an in-depth discussion of the synthetic conditions which give rise to the formation of the clusters. Each cluster subunit displays an unprecedented diequatorial substitution pattern facilitating the combination of three such units into a trimer, creating central cavities in the range 6.61-6.82 angstrom. The solid state arrangements of polyoxoanions 1, 3 and 4 are similar, but as a result of the relevant synthetic approaches, they differ greatly from that of 2. Electrochemical analysis of the new structures is detailed revealing that polyoxoanion 4 shows potential as an electrocatalyst in the reduction of nitrites.