组氨酸12-硅钨杂多酸盐超分子化合物的结构与光致变色性质

通过溶液法合成了一个新颖的组氨酸12-硅钨杂多酸盐((HisH₂)₂SiW₁₂O₄₀·6H₂O)单晶超分子化合物. 利用元素分析、热重-差热分析和X射线单晶衍射测试分别对其组成、热稳定性和结构进行了表征. 实验结果表明:该超分子化合物的组成为C₁₂H₃₄N₆O₅₀SiW₁₂. 空气中, 在135 °C以下稳定. 它属于单斜晶系(空间群为C2/c), 晶胞参数为a=2.44005(18) nm, b=1.29788(10) nm, c=1.86898(14) nm, β=124.0380(10)°, V=4.9048(6) nm³,Z=4 和D_c=4.465 g·cm^-3. 基于F²的最终统计: 拟合优度(GOF)=1.268, R₁=0.0344 和wR₂=0.0851 (I>2σ(I)). 该单晶超分子化合物的基本结构单元由一个SiW₁₂O₄₀]^4-多阴离子和两个质子化的H₂His]²⁺有机阳离子以及结晶水组成. 他们之间通过氢键的作用组装成三维网络结构. 在紫外光照射下, 样品具有光致变色性质. 通过对变色样品电子自旋共振谱的分析, 我们提出了一个可能的光致变色机理.

Structure and Photochromic Properties of a Histidine Salt of 12-Silicotungstate Supramolecular Compound

We synthesized a novel histidine salt of 12-silicotungstate supramolecular compound ((HisH₂)₂SiW₁₂O₄₀·6H₂O) by a solution method. Its composition, thermostability, and structure were characterized by elemental analysis, thermal gravimetric and differential thermal analysis (TG-DTA), and single crystal X-ray diffraction, respectively. The experimental results show that the supramolecular compound has a composition of C₁₂H₃₄N₆O₅₀SiW₁₂ and it is stable under 135 °C in air. It belongs to a monoclinic system (space group C2/c) with a=2.44005(18) nm, b=1.29788(10) nm, c=1.86898(14) nm, β=124.0380(10)°, V= 4.9048(6) nm3, Z=4, and D_c=4.465 g·cm^-3. The final statistics based on F² are goodness-of-fit (GOF) = 1.268, R₁=0.0344 and wR₂=0.0851 for (I>2σ(I)). X-ray diffraction analysis further reveals that this supramolecular compound mainly consists of polyoxometalate anions SiW₁₂O₄₀]^4-, protonated histidine cations HisH₂]²⁺ and lattice water. A three-dimensional (3D) network is formed through hydrogen bonding. The resulting sample shows photochromism under UV irradiation. We propose a possible photochromic mechanism by an analysis of the chromic sample′s electron spin resonance (ESR) spectrum.