Soluble metal-oxide frameworks: Transport of large organic guests through smaller subnanoscale pores and the effects of nano-confinement on hydrophobic self-assembly and organic reactions

在沸石和刚性功能材料中，严格排除尺寸超过孔尺寸的基材。同时，柔性金属有机框架（MOF;另一类多孔固态结构）内的空腔可以通过可逆的、逐步的结构膨胀（“呼吸”）来容纳基底。现在，使用“胶囊”样的氧化物基的框架作为多孔固态（刚性）氧化物的可溶性类似物，我们最近报道了一种新现象：支链烷烃“客体”通过柔性亚纳米Mo 9 O 9孔，其几何直径小于进入的物质（“Flexible Pores of a Metal-Oxide-Based Permit Capsule Entry of Comparatively Larger Organic Guests”J. Am.化学会，2009，131，6380-6382）。这种新的现象可能反映了分子结构相对于固态结构的更大灵活性，并且代表了与通过刚性多孔固体氧化物扩散的传统模型的明显偏离。拟议的研究的直接目标是调查的基本机制（S）负责的相对较小的金属氧化物孔的大客人的吸收。下一个目标是使用金属氧化物胶囊作为“纳米反应器”，通过近端结合的模板效应和/或胶囊的纳米限制内部的疏水自组装来催化加速反应速率。在所有上述情况下，金属氧化物框架将被部署为多孔固态金属氧化物的分子类似物，其反应及其机制现在可以通过溶液状态方法详细研究。

In zeolites and rigid functional materials, substrates whose sizes exceed those of the pore dimensions are rigorously excluded. Meanwhile, cavities within flexible metal-organic frameworks (MOFs; another class of porous solid-state structures) can accommodate substrates by reversible, stepwise structural expansion (“breathing”). Now, using a “capsule”-like molybdenum-oxide-based framework as a soluble analog of porous solid-state (rigid) oxides, we recently reported a new phenomenon: the passage of branched-alkane “guests” through flexible sub-nanometer Mo9O9 apertures whose geometrical diameters are smaller than the entering species (“Flexible Pores of a Metal-Oxide-Based Capsule Permit Entry of Comparatively Larger Organic Guests” J. Am. Chem. Soc., 2009, 131, 6380-6382). This new phenomenon likely reflects the greater flexibility of molecular versus solid-state structures, and represents a distinct departure from traditional models for diffusion through rigid porous solid-oxides. The immediate goal of proposed research is to investigate the fundamental mechanism(s) responsible for the uptake of large guests by comparatively smaller metal-oxide pores. The next objective is to use the metal-oxide capsules as “nano-reactors” for catalytic accelerations of reaction rates through the templating effects of proximal binding, and/or hydrophobic self-assembly within the capsule’s nano-confined interiors. In all the above, the metal-oxide frameworks will be deployed as molecular analogs for porous solid-state metal oxides, whose reactions and their mechanisms can now be studied in detail by solution-state methods.