Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada.
J Am Chem Soc. 2010 Mar 24;132(11):3893-908. doi: 10.1021/ja910419h.
A family of molecular heptacadmium carboxylate clusters templated inside [3 + 3] Schiff base macrocycles has been isolated and studied by variable temperature solution and solid-state NMR spectroscopy, single-crystal X-ray diffraction (SCXRD), and density functional theory (DFT) calculations. These metallocavitand cluster complexes adopt bowl-shaped structures, induced by metal coordination, giving rise to interesting host-guest and supramolecular phenomena. Specifically, dimerization of these metallocavitands yields capsules with vacant coordination and hydrogen-bonding sites accessible to encapsulated guests. Strong host-guest interactions explain the exceptionally high packing coefficient (0.80) observed for encapsulated N,N-dimethylformamide (DMF). The guest-accessible hydrogen-bonding sites arise from an unusual mu(3)-OH ligand bridging three cadmium ions. Thermodynamic and kinetic studies show that dimerization is an entropy-driven process with a highly associative mechanism. In DMF the exchange rate of peripheral cluster supporting carboxylate ligands is intrinsically linked to the rate of dimerization and these two seemingly different events have a common rate-determining step. Investigation of guest dynamics with solid-state (2)H NMR spectroscopy revealed 3-fold rotation of an encapsulated DMF molecule. These studies provide a solid understanding of the host-guest and dynamic properties of a new family of metallocavitands and may help in designing new supramolecular catalysts and materials.
一个由分子七镉羧酸簇在[3 + 3]席夫碱大环内模板化的家族已经通过变温溶液和固态 NMR 光谱、单晶 X 射线衍射 (SCXRD) 和密度泛函理论 (DFT) 计算进行了分离和研究。这些金属穴状聚集体络合物采用碗状结构，由金属配位诱导，产生有趣的主客体和超分子现象。具体来说，这些金属穴状聚集体的二聚化产生具有空配位和可容纳被包封客体的氢键结合部位的胶囊。强的主客体相互作用解释了观察到的封装 N,N-二甲基甲酰胺 (DMF) 的异常高堆积系数 (0.80)。可访问的客体氢键部位来自于一种不寻常的 μ(3)-OH 配体桥接三个镉离子。热力学和动力学研究表明，二聚化是一个熵驱动的过程，具有高度缔合的机制。在 DMF 中，外围簇支撑羧酸配体的交换速率与二聚化的速率内在相关，这两个看似不同的事件具有共同的速率决定步骤。通过固态 (2)H NMR 光谱研究客体动力学，发现被包封的 DMF 分子发生了 3 重旋转。这些研究提供了对新的金属穴状聚集体的主客体和动态性质的深入了解，并可能有助于设计新的超分子催化剂和材料。
