Lanthanide-Centered Polyoxoalkoxide Complexes Provide a Platform for Systematic Room- and Variable-Temperature Nuclear Magnetic Resonance Studies

A single, high-yielding approach was employed to synthesize the complete series of lanthanide (Ln) containing polyoxoalkoxide sandwich-type complexes (TBA)3[M{Mo5O13(OMe)4NO}2] (M = La–Lu, except Pm). The complexes were characterized by solution-state 1H/17O NMR spectroscopy, infrared spectroscopy, cyclic voltammetry, and electronic absorption spectroscopy, while the new derivatives (M = Tm, Yb, Lu, and Y) were also characterized using single crystal X-ray diffraction experiments. Compared to similar [Ln(W5O18)2]9– or [Ln(PW11O39)2]11– series, the presence of large noncoordinating tetrabutylammonium cations makes this series unique in that all (TBA)3[M{Mo5O13(OMe)4NO}2] complexes are isostructural in the solid-state, with no changes in crystal packing or polymorph across the series. Solution-state NMR investigations reveal large Ln induced shifts (ca. 100–2000 ppm) for 17O nuclei directly bound to the Ln center. Variable temperature 17O NMR spectroscopy reveals that the chemical shift these oxygen nuclei show significant temperature dependence, opening the door to 17O NMR thermometry with Ln containing polyoxometalates.