Solid State Characterization of Bridged Steroidal Molecular Rotors: Effect of the Rotator Fluorination on Their Crystallization

We describe the synthesis and crystallization of two macrocyclic steroidal compounds labeled (Z)-1F2 and (E)-1F2, envisioned to work as molecular rotors with 1,4-diethynyl-2,3-difluorophenylene rotators. The introduction of the fluorine atoms rendered different crystal arrays that were fully characterized by X-ray diffraction, solid state 13C NMR, and calorimetric experiments. In both isomers, the central molecular fragments point the o-fluorine atoms toward their cavity, highlighting the preferred orientation in the solid state. By analyzing the crystal array, it can be seen that while the fluorinated Z isomer is isomorphic to its non-fluorinated analogue, the E isomer shows significant structural variations in an unanticipated crystal array with two molecules per asymmetric unit (Z′ = 2).