Chloride Ion-Aided Self-Assembly of Pseudoclathrochelate Metal Tris-pyrazoloximates

Chloride ion-aided one-pot template
self-assembly of a mixed pyrazoloxime
ligand with phenylboronic acid on a corresponding metal­(II) ion as
a matrix afforded the first boron-capped zinc, cobalt, iron, and manganese
pseudoclathrochelate tris-pyrazoloximates. The presence of a pseudocross-linking
hydrogen-bonded chloride ion is critical for their formation, as the
same chloride-capped complexes were isolated even in the presence
of large excesses of bromide and iodide ions. As revealed by X-ray
diffraction, all complexes are capped with a chloride ion via three
N–H···Cl hydrogen bonds that stabilize their
pseudomacrobicyclic frameworks. The MN6 coordination polyhedra
possess a distorted trigonal prismatic geometry, with the distortion
angles φ between their nonequivalent N3 bases of
approximately 0°. Temperature dependences of the effective magnetic
moment for the paramagnetic complexes showed the encapsulated metal­(II)
ions to be in a high-spin state in the temperature range of 2–300
K. In the case of the iron­(II) pseudoclathrochelate, density functional
theory (DFT) and time-dependent DFT calculations were used to assess
its spin state as well as the 57Fe Mössbauer and
UV–vis–NIR parameters. Cyclic voltammetry studies performed
for these pseudomacrobicyclic complexes showed them to undergo irreversible
or quasi-reversible metal-localized oxidations and reductions. As
no changes are observed in the presence of a substantial excess of
bromide ion, no anion-exchange reaction occurs, and thus the pseudoclathrochelates
have a high affinity toward chloride anions in solution.

在对应金属(II)离子作为模板基质的条件下，借助氯离子辅助的一锅法模板自组装策略，将混合吡唑肟配体与苯硼酸结合，首次合成得到了硼封端的锌、钴、铁及锰基三吡唑肟假穴状配合物（pseudoclathrochelate）。假交联氢键合氯离子的存在对这类配合物的形成至关重要：即便体系中存在大量过量的溴离子与碘离子，仍可分离得到相同的氯离子封端配合物。经X射线衍射表征证实，所有配合物均通过三条N–H···Cl氢键与氯离子结合，以此稳定其假大环双环骨架结构。其MN6配位多面体呈现畸变三角棱柱几何构型，不等价N3配位基面间的畸变角φ约为0°。顺磁性配合物的有效磁矩随温度的变化规律表明，在2~300 K的温度区间内，被包封的金属(II)离子均处于高自旋状态。针对铁(II)假穴状配合物，研究人员借助密度泛函理论（DFT）与含时DFT计算，对其自旋状态以及57Fe穆斯堡尔谱、紫外-可见-近红外光谱参数进行了评估。对这类假大环双环配合物开展的循环伏安法研究显示，其可发生不可逆或准可逆的金属局域氧化还原反应。由于在体系中加入大量过量溴离子时未观察到任何变化，说明并未发生阴离子交换反应，因此这类假穴状配合物在溶液中对氯离子具有极高的结合亲和力。