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 {Mo132} “browns” and the toroidal {Mo154} “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: [MoV52MoVI12H26O200]42− {Mo64} and [MoV40MoVI30H30O215]20− {Mo70}, 81 % and 57 % reduced, respectively. The {Mo64} 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 {Mo70} cluster comprises five tripodal {MoV6} and five tetrahedral {MoV2MoVI2} building blocks alternatively linked to form a loop with a pentagonal star topology. We also show how the reaction yielding the {Mo64} super‐cube can be used in the enrichment of lanthanides which exploit the differences in selectivity in the self‐assembly of the polyoxometalates. Novel types of highly reduced Mo polyoxometalates, the {Mo64} cube and {Mo70} star, are obtained through near‐hydrothermal conditions with incorporations of nickel and lanthanide ions and possess a set of building blocks different to those present in Mo blues and browns. With a few of other rare structures, this group of polyoxomolybdates is redefined as Mo reds based on the major differences in building blocks and reduction degrees.