Recent advances in polyoxometalate-based lanthanide–oxo clusters

Traditional homogeneous water oxidation catalysts are plagued by instability under the reaction conditions. We report that the complex [Co4(H2O)2(PW9O34)2]10-, comprising a Co4O4 core stabilized by oxidatively resistant polytungstate ligands, is a hydrolytically and oxidatively stable homogeneous water oxidation catalyst that self-assembles in water from salts of earth-abundant elements (Co, W, and P). With [Ru(bpy)3]3+ (bpy is 2,2'-bipyridine) as the oxidant, we observe catalytic turnover frequencies for O2 production > or = 5 s(-1) at pH = 8. The rate's pH sensitivity reflects the pH dependence of the four-electron O2-H2O couple. Extensive spectroscopic, electrochemical, and inhibition studies firmly indicate that [Co4(H2O)2(PW9O34)2]10- is stable under catalytic turnover conditions: Neither hydrated cobalt ions nor cobalt hydroxide/oxide particles form in situ.

Single-molecule magnets (SMMs) containing only one metal center may represent the lower size limit for molecule-based magnetic information storage materials. Their current drawback is that all SMMs require liquid-helium cooling to show magnetic memory effects. We now report a chemical strategy to access the dysprosium metallocene cation [(CpiPr5)Dy(Cp*)]+ (CpiPr5 = penta-iso-propylcyclopentadienyl, Cp* = pentamethylcyclopentadienyl), which displays magnetic hysteresis above liquid-nitrogen temperatures. An effective energy barrier to reversal of the magnetization of Ueff = 1,541 cm–1 is also measured. The magnetic blocking temperature of TB = 80 K for this cation overcomes an essential barrier towards the development of nanomagnet devices that function at practical temperatures.

[ErW10O36]9- is the first polyoxometalate behaving as a single-molecule magnet (SMM). It shows frequency-dependent out-of-phase magnetization and a thermally activated single relaxation process with an effective barrier of 55.8 K. This single lanthanide ion polyoxometalate is the inorganic analogue of the bis(phthalocyaninato)lanthanide SMMs, both exhibiting very similar ligand field symmetries around the lanthanide ion (idealized D4d). It is chemically stable and offers new avenues for organization and processing of single-molecule magnets. Furthermore, it can be made free from nuclear spins and opens the possibility to be used for studies of decoherence on unimolecular qubits.