Structural and Vibrational Properties of Lanthanide Lindqvist Polyoxometalate Complexes

13 March 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


Molecular spin qubits have demonstrated immense potential in quantum information science research due to the addressability of electron spins using microwave frequencies, and the scalability and tunability of molecular systems. Exemplary in this regard is the holmium polyoxometalate, [Na9Ho(W5O18)2]•35H2O (HoW10), which features an accessible atomic clock transition at 9.4 GHz; however, the coherence time of this molecule is limited by spin-phonon coupling driven decoherence processes. To limit these decoherence pathways, materials need to be designed to reduce energy overlap between spin and phonon states, and this necessitates developing a better understanding on how structural modifications impact the vibrational landscape for classes of complexes. Herein we conducted a full investigation into the fundamental structural and vibrational properties of the lanthanide Lindqvist polyoxometalate series, [Na9Ln(W5O18)2]•XH2O (Ln = La(III) – Lu(III), except Pm(III)) (LnW10), to assess how structural changes effect vibrational characteristics and to elucidate pathways to improve the coherence properties of HoW10. Single crystal X-ray diffraction results revealed four distinct structural polymorphs in complexes 1-14 wherein first coordination spheres were identical, and differences manifested as changes in lattice packing. Interestingly, the subtle changes in packing exhibited by the four polymorphs were found to impact distortions away from ideal D4d symmetry for each of the LnW10 complexes. Raman and far-infrared spectra of complexes 1-14 were collected to identify vibrational modes present in low energy regions and peak fitting and assignments were made according to literature precedence. Qualitative and Partial Least Squares (PLS) analysis show correlations between complex structural parameters with the low energy Raman and FIR vibrational modes of interest. Overall, this investigation shows that the second coordination sphere plays an integral role in modulation of the structural and vibrational characteristics of LnW10 complexes, which makes it a viable route for tuning spin and vibrational manifolds of species within this series.


Quantum Information Science
Vibrational Spectroscopy
Spin-Phonon Coupling

Supplementary materials

Supporting Information
Supporting data includes crystallographic parameters for complexes 1-14, additional structural figures, methodological details for determining structural distortion parameters, raw and fitted FIR and Raman spectra for complexes 1-14, plots comparing structural distortion parameters versus lanthanide ionic radii, plots comparing FIR and Raman vibrational modes frequencies with structural distortion parameters, methodological details for performing PLS analysis, and plots produced from PLS analysis where the relationship between FIR and Raman vibrational modes frequencies and structural distortion parameters was investigated. The CIFs for complexes 1-14 have also been deposited at the Cambridge Crystallographic Database Centre and may be obtained from by citing reference numbers 2336257 (complex 9), 2336260 – 2336262 (complexes 3, 8, and 12), 2336274 – 2336276 (complexes 5, 6, and 13), 2336278 (complex 7), 2336280 (complex 11), 2336284 (complex 1), 2336286 (complex 2), 2336288 (complex 14), 2336290 (complex 4), and 2336921 (complex 10).


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