Compression of Molybdenum Blue Polyoxometalate Cluster Rings

The self-assembly of polyoxometalate (POM) clusters remains challenging because they heavily depend on highly sensitive synthetic conditions that produce a vast library of potential building blocks and subunits such that explicit control is hard. This work reports new strategies to construct compressed molybdenum blue (MB) type cluster rings with a new range of giant MB POM clusters {Mo₅₄}, {Mo₅₈}, {Mo₈₅}, and {Mo₁₀₈}. These MB clusters prove the limits of the ring structure archetype, showing that it is possible to compress the ring by 100 metal atoms from 154 to 54 yet keep the electronic structure and ring shape. These structures comprise distorted pentagonal building blocks. The compression of the ring is achieved by using a {Mo₃S} unit and {Mo₅} bridging units. The {Mo₈₅} and {Mo₁₀₈} clusters exhibit a unique closed architecture, and redox studies demonstrate the reduced nature of these clusters.