Capsule Formation, Carboxylate Exchange, and DFT Exploration of Cadmium Cluster Metallocavitands: Highly Dynamic Supramolecules

详细信息    查看全文

• 作者：Peter D. Frischmann ; Glenn A. Facey ; Phuong Y. Ghi ; Amanda J. Gallant ; David L. Bryce ; Francesco Lelj ; Mark J. MacLachlan
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：March 24, 2010
• 年：2010
• 卷：132
• 期：11
• 页码：3893-3908
• 全文大小：702K
• 年卷期：v.132,no.11(March 24, 2010)
• ISSN：1520-5126

文摘

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 μ₃-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 ²H 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.