Molecular spin qubits based on molecules that feature accessible atomic clock transitions have demonstrated immense potential in quantum information science research, and exemplary in this regard is the holmium polyoxometalate, [Na9Ho(W5O18)2]•35H2O (HoW10). The coherence time of this molecule is limited by spin-phonon coupling driven decoherence processes, and one route to overcome this limitation is to increase the magnetic anisotropy of the metal included within the polyoxometalate (POM) complex. Herein we conducted a full investigation into the fundamental structural and vibrational properties of Lindqvist POMs that include uranium (IV), which also feature MJ = ± 4 ground states, similar to Ho(III) in HoW10. Based on recent results from our group that demonstrated the importance of the secondary lattice elements in tuning the distortion of the D4d symmetry in W10 POM complexes, we synthesized eight UW10 complexes with different alkali metal counterions and evaluated how the composition and packing of counterion species affected complex structural and vibrational properties Single crystal X-ray diffraction analysis on complexes 1-8 revealed changes in structural distortion parameters, i.e., skew angle, plane angle, and plane distance, as a function of differences in counterion configurations. Far-infrared and Raman spectra for 1-8 also demonstrated that vibrational mode frequencies [ν(WO5)2, ρ(UO8), ν/ρ(UO8), δ/ρ(UO4), POM deformation mode, δ(W-O-W/W=O/U-O-W), ν(W-O-W), and ν(U-O-W)] were sensitive to changes in counterion composition and packing. To more effectively compare different counterions configuration we developed counterion effective ionic radius (eIR) as a new structural parameter and comparisons between structural distortion parameters and counterion eIR strongly suggest modulation by the secondary lattice elements can affect structural and vibrational manifolds within POM complexes. Partial Least Squares (PLS) analysis was used to quantitatively evaluate correlations observed within this investigation, and PLS statistical models showed strong correlation between counterion eIR and both structural distortion parameters and vibrational mode frequencies. Overall, this investigation illustrates how to diversify the composition of lattice elements within UW10 complexes and confirms the integral role counterions play in modulating the structural and vibrational characteristics of Lindqvist POM complexes with f-elements.

中文翻译：

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描述反离子对 U（IV） Lindqvist 多金属氧酸盐配合物结构和振动性能的影响


基于具有可访问原子钟跃迁的分子的分子自旋量子比特在量子信息科学研究中显示出巨大的潜力，这方面的代表是多金属氧钬 [Na9Ho（W5O18）2]•35H2O （HoW10）。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，克服此限制的一种方法是增加多金属氧酸盐 （POM） 络合物中包含的金属的磁各向异性。在本文中，我们对包括铀 （IV） 在内的 Lindqvist POM 的基本结构和振动特性进行了全面研究，铀 （IV） 还具有 MJ = ± 4 个基态，类似于 HoW10 中的 Ho（III）。根据我们小组最近的结果，证明了次级晶格元件在调节 W10 POM 配合物中 D4d 对称性失真中的重要性，我们合成了八种具有不同碱金属对抗离子的 UW10 配合物，并评估了对抗离子种类的组成和堆积如何影响配合物结构和振动特性配合物 1-8 的单晶 X 射线衍射分析揭示了结构变形参数的变化， 即偏斜角、平面角和平面距离，作为对离子构型差异的函数。1-8 的远红外和拉曼光谱还表明，振动模式频率 [ν（WO5）2， ρ（UO8）， ν/ρ（UO8）， δ/ρ（UO4）， POM 变形模式， δ（W-O-W/W=O/U-O-W）， ν（W-O-W） 和 ν（U-O-W）] 对反离子组成和堆积的变化很敏感。 为了更有效地比较不同的反离子构型，我们开发了反离子有效离子半径 （eIR） 作为一种新的结构参数，结构变形参数和反离子 eIR 之间的比较强烈表明，次级晶格元件的调制会影响 POM 配合物内的结构和振动流形。偏最小二乘法 （PLS） 分析用于定量评估本研究中观察到的相关性，PLS 统计模型显示反离子 eIR 与结构变形参数和振动模式频率之间具有很强的相关性。总体而言，这项研究说明了如何使 UW10 配合物中晶格元件的组成多样化，并证实了反离子在调节具有 f 元件的 Lindqvist POM 配合物的结构和振动特性中发挥的不可或缺的作用。