Thermal spin-crossover in the [M3Zn6Cl6L12] (M = Zn, FeII; L = 5,6-dimethoxy-1,2,3-benzotriazolate) system: structural, electrochemical, Mössbauer, and UV-Vis spectroscopic studies
作者:Shyam Biswas、Markus Tonigold、Harald Kelm、Hans-Jörg Krüger、Dirk Volkmer
DOI:10.1039/c0dt00556h
日期:——
Fusion of pentanuclear Kuratowski-type coordination units leads to homo- and heterononanuclear coordination compounds, two of which are presented, having structural formulae [Zn9Cl6(OMe2bta)12]·DMF (1), and [FeII3Zn6Cl6(OMe2bta)12]·DMF (2), respectively; (OMe2btaH = 5,6-dimethoxy-1,2,3-benzotriazole; DMF = N,N′-dimethylformamide). Single crystal X-ray structure analyses reveal the presence of M3Zn6L12}6+ cores (M = Zn or FeII; L = 5,6-dimethoxy-1,2,3-benzotriazolate) in which the MII ions are bridged by μ3-OMe2bta ligands. In both compounds, the six peripheral Zn ions are tetracoordinated, whereas the remaining three metal ions M are hexacoordinated. The charge of each M3Zn6L12}6+ moiety is balanced by six chloride anions that are monodentately bound to the peripheral Zn ions. Based on differences in experimental Fe–N-donor bond lengths (deduced from single crystal data of 2 recorded at 223 K), two out of three FeII ions are found in a high-spin (HS) state, whereas one FeII ion shows a low-spin (LS) state. The assignment of different energetic ground states of FeII ions is corroborated by spectroscopic studies: Both solid-state and solution UV-Vis spectra of 2 (at ambient temperature) display absorption bands owing to the presence of both HS and LS FeII ions. Removal of occluded DMF molecules from the crystal lattices of 1 and 2 in high vacuum leads to fully desolvated powders, termed hereafter 1a and 2a, respectively. Mössbauer studies on 2a show that all three FeII ions are in HS state at 160 K, and upon cooling to 7 K, the central FeII ion undergoes a HS→LS transition while the HS states of the other FeII ions remains unchanged. The cyclic voltammogram of 2 (chloroform solution) exhibits a single reversible oxidation regardless of different FeII spin states in the nonanuclear core of 2.
五核 Kuratowski 型配位单元的融合产生了同核和异核配位化合物,其中两种化合物的结构式分别为 [Zn9Cl6(OMe2bta)12]-DMF (1) 和 [FeII3Zn6Cl6(OMe2bta)12]-DMF (2);(OMe2btaH=5,6-二甲氧基-1,2,3-苯并三唑;DMF=N,N′-二甲基甲酰胺)。单晶 X 射线结构分析表明存在 M3Zn6L12}6+ 核心(M = Zn 或 FeII;L = 5,6-二甲氧基-1,2,3-苯并三唑),其中 MII 离子由 μ3-OMe2bta 配体桥接。在这两种化合物中,六个外围 Zn 离子是四配位的,而其余三个金属离子 M 是六配位的。每个M3Zn6L12}6+分子的电荷通过与外围 Zn 离子单价结合的六个氯阴离子来平衡。根据实验中 Fe-N-捐赠者键长的差异(根据在 223 K 下记录的 2 的单晶数据推断),发现三个 FeII 离子中有两个处于高自旋(HS)状态,而一个 FeII 离子则处于低自旋(LS)状态。光谱研究证实了 FeII 离子处于不同的高能基态:2 的固态和溶液紫外可见光谱(环境温度下)都显示出 HS 和 LS 两种 FeII 离子的吸收带。在高真空条件下从 1 和 2 的晶格中去除闭塞的 DMF 分子,可得到完全脱溶的粉末,以下分别称为 1a 和 2a。对 2a 的莫斯鲍尔研究表明,在 160 K 时,所有三个 FeII 离子都处于 HS 状态,冷却到 7 K 时,中心的 FeII 离子发生了 HS→LS 转变,而其他 FeII 离子的 HS 状态保持不变。2 的循环伏安图(氯仿溶液)显示出单一的可逆氧化,与 2 的非核心中不同的 FeII 自旋态无关。