Coordinative Alignment in the Pores of MOFs for the Structural Determination of N‑, S‑, and P‑Containing Organic Compounds Including Complex Chiral Molecules

Coordinative alignment of target small molecules onto
a chiral
metal–organic framework (MOF-520)­provides a powerful method
to determine the structures of small molecules through single-crystal
X-ray diffraction (SXRD). In this work, the structures of 17 molecules
with eight new coordinating functionalities and varying size have
been determined by this method, four of which are complex molecules
being crystallized for the first time. The chirality of the MOF backbone
not only enables enantioselective crystallization of chiral small
molecules from a racemic mixture but also imposes diastereoselective
incorporation upon achiral molecules. Crystallographic studies assisted
by density functional theory (DFT) calculations indicate that the
stereoselectivity of MOF-520 not exclusively comes from the steric
confinement of the chiral pore environment but also from asymmetric
chemical bonding of the target molecules with the framework that is
able to provide sufficient energy difference between possible coordination
configurations.

将目标小分子配位固定于手性金属有机框架（metal–organic framework, MOF-520）之上，是一种借助单晶X射线衍射（single-crystal X-ray diffraction, SXRD）测定小分子晶体结构的高效手段。本研究通过该方法解析了17种分子的晶体结构，这些分子具备八种新型配位官能团且尺寸各异，其中四种为首次获得结晶的复杂分子。该金属有机框架骨架的手性不仅可实现外消旋混合物中手性小分子的对映选择性结晶，还能赋予非手性分子非对映选择性结合的特性。结合密度泛函理论（density functional theory, DFT）计算的晶体学研究表明，MOF-520的立体选择性并非仅来源于手性孔道环境的空间限域效应，还源于目标分子与框架之间的不对称化学键合作用——这类作用可在不同潜在配位构型间形成足够的能量差。