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，尺寸超过孔尺寸的基质被严格排除在外。同时，柔性金属有机骨架(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”)来容纳衬底。现在，我们利用一种“胶囊”状的氧化钼骨架作为多孔固体(刚性)氧化物的可溶类似物，最近报道了一种新的现象：支链烷烃“客体”通过几何直径小于进入物种的柔性亚纳米Mo9O9孔(“金属氧化物胶囊的柔性孔允许相对较大的有机客体进入”J.Am化学。SoC.，2009,131,6380-6382)。这一新现象可能反映了分子结构与固态结构相比具有更大的灵活性，并与传统的通过硬质多孔固体氧化物扩散的模型截然不同。拟议研究的直接目标是调查相对较小的金属氧化物气孔吸收大客体的基本机制(S)。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/或胶囊纳米限制内部的疏水自组装作用来催化加速反应速度。综上所述，金属氧化物骨架将被用作多孔固态金属氧化物的分子模拟物，其反应及其机理现在可以用溶液状态方法进行详细的研究。

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.