Dynamics of Organic Cations in Switchable Quinuclidinium Metal Chloride Dielectrics

The synthesis and structure of a series of quinuclidinium-based
organic–inorganic hybrids of Q2CuCl4,
Q2CoCl4, and Q4Pb3Cl10 are reported (Q = quinuclidinium, C7H13NH+). The dynamic disorder observed in the structure of
quinuclidinium metal chlorides was investigated using variable-temperature
single-crystal X-ray diffraction, IR, Raman, NMR, and dielectric spectroscopy.
The crystals undergo phase transitions (PTs) where an order–disorder
process takes place. However, it is assumed that in the case of Q2CoCl4 and Q2CuCl4, the reorientation
of Q cations is a major force driving PT, while in Q4Pb3Cl10, the reorientation of inorganic ions (Pb–Cl
moieties) is at least equally important. All three hybrid compounds
exhibit switchable and tunable properties of the dielectric function
between two stable ON/OFF states. The magnetic properties were also
investigated over a wide temperature range by measuring the magnetic
susceptibility and magnetization as a function of temperature and
external magnetic field, which allowed us to demonstrate the competition
between the paramagnetic and diamagnetic signals in these compounds.
The dynamics probed by NMR has shown a nonequivalence of Q cations
in all studied compounds.

本文报道了一系列基于奎宁环鎓（quinuclidinium）的有机-无机杂化材料，其通式为Q₂CuCl₄、Q₂CoCl₄及Q₄Pb₃Cl₁₀（其中Q为奎宁环鎓阳离子，即C₇H₁₃NH⁺）。本研究借助变温单晶X射线衍射、红外（IR）光谱、拉曼（Raman）光谱、核磁共振（NMR）谱以及介电光谱，对奎宁环鎓金属氯化物结构中存在的动态无序现象展开了探究。该类晶体均会发生有序-无序转变类型的相变（PTs）。不过研究认为，对于Q₂CoCl₄与Q₂CuCl₄而言，Q阳离子的重新取向是驱动其相变的核心因素；而对于Q₄Pb₃Cl₁₀来说，无机离子（Pb-Cl基团）的重新取向同样起到了关键作用，二者的贡献至少不相上下。上述三种杂化材料均展现出可切换、可调谐的介电函数特性，其介电响应可在两种稳定的“通/断”（ON/OFF）状态间切换。本研究还通过在宽温区间内测试磁化率与磁化强度随温度及外磁场的变化关系，对这三种材料的磁学特性展开了探究，由此证实了此类化合物中顺磁信号与抗磁信号之间的竞争行为。通过核磁共振（NMR）探测得到的动力学行为表明，所有被测样品中的Q阳离子均存在化学不等价性。