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.