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 D_4d symmetry for each of the LnW₁₀ complexes. Raman and far-infrared (FIR) spectra of complexes 1–14 were collected to identify vibrational modes present in low energy regions and peak fitting assignments were made according to literature precedents. 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.

中文翻译：

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镧系 Lindqvist 多金属氧酸盐配合物的结构和振动特性


由于使用微波频率的电子自旋的可寻址性以及分子系统的可扩展性和可调谐性，分子自旋量子位在量子信息科学研究中表现出了巨大的潜力。这方面的例子是多金属氧酸钬，[Na ₉ Ho(W ₅ O ₁₈ ) ₂ ]·35H ₂ O (HoW ₁₀ )，其特点是可在 9.4 GHz 处实现原子钟跃迁；然而，该分子的相干时间受到自旋声子耦合驱动的退相干过程的限制。为了限制这些退相干路径，需要设计材料来减少自旋态和声子态之间的能量重叠，这需要更好地理解结构修饰如何影响复合物类别的振动景观。在此，我们对镧系元素 Lindqvist 多金属氧酸盐系列的基本结构和振动特性进行了全面的研究，[Na ₉ Ln(W ₅ O ₁₈ ) ₂ ]·xH ₂ O (Ln = La(III)–Lu(III)，Pm(III) 除外) (LnW ₁₀ )，评估结构如何变化影响振动特性并阐明改善 HoW ₁₀ 相干特性的途径。单晶X射线衍射结果显示配合物1-14中有四种不同的结构多晶型物，其中第一配位球是相同的，差异表现为晶格堆积的变化。有趣的是，我们发现四种多晶型物在堆积方面的细微变化会影响每种 LnW ₁₀ 配合物偏离理想 D _4d 对称性的扭曲。 收集配合物 1-14 的拉曼和远红外 (FIR) 光谱，以识别低能区域中存在的振动模式，并根据文献先例进行峰值拟合分配。定性和偏最小二乘 (PLS) 分析显示复杂结构参数与感兴趣的低能拉曼和 FIR 振动模式之间的相关性。总体而言，这项研究表明，第二配位层在 LnW ₁₀ 配合物的结构和振动特性的调节中发挥着不可或缺的作用，这使其成为调节该系列物质的自旋和振动流形的可行途径。