Isomerization of Na-Centered Alkyltin Keggin Clusters

The Keggin cluster topology, discovered in tungsten polyoxometalates approximately a century ago, is now broadly represented across the periodic table. The alkyltin Keggin clusters are unique in that it is the only Keggin family that appears to favor the rarer beta and gamma rotational isomers, co-crystallized as beta,gamma-[(BuSn)(12)(NaO4)(OCH3)(12)(O)(5)(OH)(7)] (beta,gamma-NaSn12). Nuclear Magnetic Resonance Spectroscopy (NMR; H-1, Sn-119) studies show lability and ready exchange between hydroxy-methoxy ligands, accelerated by residual water in polar solvents. Room temperature and heated solutions of beta,gamma-NaSn12 show five distinct Na-23 NMR peaks, corresponding to all five of the Keggin rotational isomers simultaneously in solution. This is the only example of coexistence of all Keggin isomers simultaneously, providing more in-depth insight into parameters influencing Keggin isomer stabilization, isolation, and exchange.

Automated summary

The Keggin cluster topology, initially discovered in tungsten polyoxometalates about a century ago, is widely represented across the periodic table. Alkyltin Keggin clusters, unique in favoring rare beta and gamma rotational isomers, show lability and ready exchange of ligands under the influence of residual water in polar solvents. Room temperature and heated solutions of beta,gamma-NaSn12 exhibit all five Keggin rotational isomers simultaneously, providing unique insight into their stabilization, isolation, and exchange.