Electron Paramagnetic Resonance Characteristics and Crystal Structure of a Tutton Salt Analogue: Copper-Doped Cadmium Creatininium Sulfate

Electron paramagnetic resonance and
crystallographic studies on
copper-doped cadmium creatininium sulfate (CdCrnS) were undertaken
to study the characteristics of a copper-hexahydrate complex in an
organic analogue of Tutton’s salt. X-ray diffraction experiments
determined the crystal structure of CdCrnS at both 100 and 298 K.
CdCrnS, like Tutton salt, crystallizes in the monoclinic space group P21/n. The unit cell contains
two cadmium hexahydrate complexes, four creatininium ions, four sulfates,
and four additional solvation waters. Both crystallography and EPR
find that the doped copper replaces the cadmium in the structure.
Single-crystal EPR measurements at room temperature determined the g and copper hyperfine (ACu) tensors
(principal values: g = 2.437, 2.134, and 2.080 and ACu = −327, −84.8, and 7.33 MHz).
EPR spectra of the powder at room temperature gave g =
2.448, 2.125, and 2.085 and ACu = −315,
−75.0, and 35.0 MHz and at 110 K gave g = 2.462,
2.116, and 2.077 and ACu = −340, −30.0,
and 35.0 MHz. The room-temperature tensors are close to the “rigid
lattice limit” values found in copper-doped Tutton salts but
with a higher gmin and weaker ACux coupling than average.
A small but measurable temperature dependency of the tensors indicated
the presence of a dynamic Jahn-Teller (JT) effect. In addition, the
EPR line width changed dramatically with temperature, which is like
that found in all copper-doped Tutton crystals. Utilizing the model
of Silver–Getz for the g-value variation gave
an estimate for the energy difference (δ12 = 640
cm–1) between the ground and next highest JT configurations.
An empirical correlation appears to exist between δ12 and gmin and ACux for the copper hexahydrates studied
in similar crystals. This suggests a relationship between the amount
of unpaired spins in the copper d-orbital x lobe
and the gap between wells of the adiabatic potential surface.

针对掺铜肌酐酸镉（cadmium creatininium sulfate, CdCrnS）开展电子顺磁共振（Electron paramagnetic resonance, EPR）与晶体学研究，以探究塔顿盐（Tutton’s salt）有机类似物中铜六水配合物的结构特性。X射线衍射实验分别在100 K与298 K温度下测定了CdCrnS的晶体结构。与塔顿盐一致，CdCrnS以单斜晶系空间群P2₁/n结晶。其晶胞包含2个六水合镉配合物、4个肌酐离子、4个硫酸根以及4个额外溶剂化水分子。晶体学与EPR测试结果均表明，掺杂的铜离子取代了晶体结构中的镉离子位点。室温下的单晶EPR测试得到了g张量与铜超精细（A_Cu）张量的主值：g分别为2.437、2.134与2.080，A_Cu分别为-327、-84.8与7.33 MHz。室温下的粉末EPR谱测得g值为2.448、2.125与2.085，A_Cu值为-315、-75.0与35.0 MHz；110 K下测得g值为2.462、2.116与2.077，A_Cu值为-340、-30.0与35.0 MHz。室温下的张量结果与掺铜塔顿盐中的“刚性晶格极限”值相近，但g_min更高且A_Cu_x耦合强度弱于平均水平。该张量存在微弱但可观测的温度依赖性，表明存在动态姜-泰勒（Jahn-Teller, JT）效应。此外，EPR谱线宽度随温度发生显著变化，这一现象与所有掺铜塔顿晶体的观测结果一致。利用Silver–Getz模型拟合g值的变化规律，估算得到基态与次高姜-泰勒构型间的能量差δ₁₂=640 cm⁻¹。针对类似晶体中研究的六水合铜配合物，δ₁₂与g_min以及A_Cu_x之间似乎存在经验相关性。这暗示铜d轨道x瓣中的未成对自旋量与绝热势能面势阱间的能隙存在关联。