Conformational Polymorphism and Isomorphism of Molecular Rotors with Fluoroaromatic Rotators and Mestranol Stators

We report the synthesis and characterization
of four molecular
rotors 2, 3, 4, and 5 containing 2-fluoro-, 2,3-difluoro-, 2,5-difluoro-, and 2,3,5,6-tetrafluoro-substituted
1,4-phenylene rotators, respectively, that are axially linked through
the triple bonds of rigid mestranol (3-methoxy-17α-ethynylestradiol)
stators. Crystallization experiments using solvent mixtures of hexanes–ethyl
acetate and acetonitrile–dichloromethane gave rise to polymorphic,
pseudopolymorphic, and isomorphic crystals. Whereas two solids were
obtained for compound 2, four were indentified in the
cases of compounds 3 and 4, and three for
compound 5. The 13 solid forms were characterized by
single-crystal and powder X-ray diffraction, infrared spectroscopy,
differential scanning calorimetry, and thermogravimetric analysis.
Two sets of isomorphous structures were obtained for solvated and
solvent-free structures of compounds 3–5. While polymorphic behavior of these compounds arises from their
conformational freedom in solution, their isomorphism arises from
the closely isosteric relation that exists between hydrogen and fluorine
atoms.

本研究报道了4种分子转子（编号2、3、4、5）的合成与表征：它们分别带有2-氟取代、2,3-二氟取代、2,5-二氟取代以及2,3,5,6-四氟取代的1,4-亚苯基转子基团，并通过刚性炔雌醇甲醚（3-甲氧基-17α-乙炔基雌二醇）定子的三键进行轴向连接。采用正己烷-乙酸乙酯、乙腈-二氯甲烷混合溶剂开展的结晶实验，得到了多晶型、假多晶型以及同晶型晶体。其中化合物2获得了2种固态形式，化合物3和4分别得到4种固态形式，化合物5则得到3种固态形式。通过单晶X射线衍射、粉末X射线衍射、红外光谱、差示扫描量热法以及热重分析对这13种固态形式进行了表征。针对化合物3至5，分别得到了溶剂化与无溶剂两种类型的同晶结构。这类化合物的多晶型行为源于其在溶液中的构象自由度，而同晶型现象则源于氢原子与氟原子之间极为相近的等排关系。