Influence of Lattice Interactions on the Jahn−Teller Distortion of the [Cu(H2O)6]2+ Ion: Dependence of the Crystal Structure of K2[Cu(H2O)6](SO4)2x(SeO4)2-2x upon the Sulfate/Selenate Ratio

The temperature dependence of the structure of the mixed-anion Tutton salt K2[Cu(H2O)6](SO4)2x(SeO4)2-2x has
been determined for crystals with 0, 17, 25, 68, 78, and 100% sulfate over the temperature range of 85−320 K.
In every case, the [Cu(H2O)6]2+ ion adopts a tetragonally elongated coordination geometry with an orthorhombic
distortion. However, for the compounds with 0, 17, and 25% sulfate, the long and intermediate bonds occur on a
different pair of water molecules from those with 68, 78, and 100% sulfate. A thermal equilibrium between the two
forms is observed for each crystal, with this developing more readily as the proportions of the two counterions
become more similar. Attempts to prepare a crystal with approximately equal amounts of sulfate and selenate were
unsuccessful. The temperature dependence of the bond lengths has been analyzed using a model in which the
Jahn−Teller potential surface of the [Cu(H2O)6]2+ ion is perturbed by a lattice-strain interaction. The magnitude and
sign of the orthorhombic component of this strain interaction depends on the proportion of sulfate to selenate.
Significant deviations from Boltzmann statistics are observed for those crystals exhibiting a large temperature
dependence of the average bond lengths, and this may be explained by cooperative interactions between neighboring
complexes.

本研究确定了混合阴离子Tutton盐K2[Cu(H2O)6](SO4)2x(SeO4)2-2x在85−320 K温度范围内，其结构随硫酸根含量的变化（0%，17%，25%，68%，78%，及100%）所呈现的温度依赖性。在所有情况下，[Cu(H2O)6]2+离子均采取四角形延长的配位几何形状，并伴随正交畸变。然而，对于硫酸根含量为0%，17%，及25%的化合物，长键和中间键出现在不同于硫酸根含量为68%，78%，及100%的化合物的不同水分子对上。每种晶体均观察到两种形态之间的热力学平衡，且随着两种反离子的比例趋于相似，这种平衡更容易形成。尝试制备硫酸根和硒酸盐含量大致相等的晶体未能成功。利用一个模型分析了键长随温度变化的关系，该模型通过晶格应变相互作用扰动[Cu(H2O)6]2+离子的Jahn−Teller势面。此应变相互作用的正交分量的大小和符号取决于硫酸根与硒酸盐的比例。观察到对于那些平均键长温度依赖性较大的晶体，其与玻尔兹曼统计存在显著偏差，这或许可以归因于邻近复杂体之间的协同作用。