Controlling the Minimal Self Assembly of “Complex” Polyoxometalate Clusters

Despite
the vast number of polyoxometalate clusters now known,
an ongoing and important challenge is to understand causality in the
assembly of “complex” clusters at a mechanistic level,
since this is the only way the rational, targeted synthesis of new
compounds will ever be achieved. Often, the complexity of the reactions
themselves makes such investigations near impossible, as very small
changes can often make dramatic differences. Herein, we explore a
very simple [A + B] binary synthetic system that gives rise to the
facile assembly of two isomeric anions, [FeIII(H2O)2{γ-FeIIISiW9O34(H2O)}2]11– (1) and [FeIII(H2O)2{γ-FeIII2SiW8O33(H2O)2}­{γ-SiW10O35}]11– (2), which can be formed as individual and dimeric
species (3) and (4). Furthermore, the simple
binary nature of this synthetic system allowed its investigation by
a comprehensive time-resolved ESI-MS analysis, yielding unprecedented
mechanistic information regarding the initial interactions and reorganizations
of the {γ-SiW10} precursor in the presence of Fe2+.