Engineering Highly Reduced Molybdenum Polyoxometalates via the Incorporation of d and f Block Metal Ions

The assembly of nanoscale polyoxometalate (POM) clusters has been dominated by the highly reduced icosahedral {Mo(132)} “browns” and the toroidal {Mo(154)} “blues” which are 45 % and 18 % reduced, respectively. We hypothesised that there is space for a greater diversity of structures in this immediate reduction zone. Here we show it is possible to make highly reduced mix‐valence POMs by presenting new classes of polyoxomolybdates: [Mo(V) (52)Mo(VI) (12)H(26)O(200)](42−) {Mo(64)} and [Mo(V) (40)Mo(VI) (30)H(30)O(215)](20−) {Mo(70)}, 81 % and 57 % reduced, respectively. The {Mo(64)} cluster archetype has a super‐cube structure and is composed of five different types of building blocks, each arranged in overlayed Archimedean or Platonic polyhedra. The {Mo(70)} cluster comprises five tripodal {Mo(V) (6)} and five tetrahedral {Mo(V) (2)Mo(VI) (2)} building blocks alternatively linked to form a loop with a pentagonal star topology. We also show how the reaction yielding the {Mo(64)} super‐cube can be used in the enrichment of lanthanides which exploit the differences in selectivity in the self‐assembly of the polyoxometalates.