One-Pot versus Sequential Reactions in the Self-Assembly of Gigantic Nanoscale Polyoxotungstates

By using a new type of lacunary tungstoselenite {Se2W29O103} (1), which contains a "defect" pentagonal {W(W)(4)} unit, we explored the assembly of clusters using this building block and demonstrate how this unit can give rise to gigantic nanomolecular species, using both a "one-pot" and "stepwise" synthetic assembly approach. Specifically, exploration of the one-pot synthetic parameter space lead to the discovery of {Co-2.5(W3.5O14)(SeW9O33)(Se2W30O107)} (2), {CoWO-(H2O)(3)(Se2W26O85)(Se3W30O107)(2)} (3), and {Ni2W2O2Cl(H2O)(3)(Se2W29O103) (Se3W30O107)(2)} (4), effectively demonstrating the potential of the {Se2W29} based building blocks, which was further extended by the isolation of a range of 3d transition metal doped tetramer family derivatives: {M2WnOm(H2O)(m)(Se2W29O102)(4)} (M = Mn, Co, Ni or Zn, n = 2, m = 4; M = Cu, n = 3, m = 5) (5 - 9). To contrast the 'one-pot' approach, an optimized stepwise self-assembly investigation utilizing 1 as a precursor was performed showing that the high nuclearity clusters can condense in a more controllable way allowing the tetrameric clusters (5 - 8) to be synthesized with higher yield, but it was also shown that 1 can be used to construct a gigantic {W-174} hexameric-cluster {Cu9Cl3(H2O)(18)(Se2W29O102)(6)} (10). Further, 1 can also dimerize to {(Se2W30O105)(2)} (11) by addition of extra tungstate under similar conditions. All the clusters were characterized by single-crystal X-ray crystallography, chemical analysis, infrared spectroscopy, thermogravimetric analysis, and electrospray ionization mass spectrometry, which remarkably showed that all the clusters, even the largest cluster, 10 (similar to 50 kD), could be observed as the intact cluster demonstrating the extraordinary potential of this approach to construct robust gigantic nanoscale polyoxotungstates.