Transition-metal substituted polyoxotungstates (TMSPOTs), when transferred into nonpolar solvents, have been reported by several groups as potential catalysts for carbon dioxide reduction. Therefore, their structures in nonpolar solvents are of great interest. Based on 31P NMR, UV/VIS, and DFT computations we suggested recently that cobalt-substituted phosphotungstate with Keggin structure (PW11CoO39) forms dimers in a dry toluene. This poster reports 31P 2D DOSY NMR measurements which demonstrate the existence of species with diffusion coefficient ratio approximately equal to the ratio of radii for dimers and monomers of tetraheptylammonium salts of PW11Co. This constitutes a direct evidence for dimer formation by TMSPOTs in toluene. After coordinated water leaves cobalt in dry toluene, an oxide ion from a second PW11Co coordinates to that cobalt, leading to dimer formation. On the other hand, we suspected that TMSPOT with two water molecules coordinated to two cobalt atoms [P2W18Co4O68(H2O)2] forms trimers in dry toluene. 31P 2D DOSY NMR indeed demonstrates the existence of species in dry toluene with diffusion coefficient ratio predicted for trimers and monomers of that compound.

Direct 2D DOSY NMR evidence for oligomer formation by transition-metal substituted polyoxotungstates in nonpolar solvents

251st National Meeting (2016)

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