Ultra-fast Rotors for Molecular Machines and Functional Materials via Halogen Bonding: Crystals of 1,4-Bis(iodoethynyl)bicyclo[2.2.2]octane with Distinct Gigahertz Rotation at Two Sites

• DOI: 10.1021/ja200503j
• Publication Date: 2011-04-06T13:10:38Z
• Authors: Cyprien Lemouchi; Cortnie S. Vogels...; Leokadiya Zorina; Sergey Simonov; Patrick Batail; Stuart Brown; Miguel A. Garcia-...
• Keywords: Monoclinic crystal system; Triclinic crystal system; Molecular solid; Atmospheric temperature range

As a point of entry to investigate the potential halogen-bonding interactions in construction functional materials and crystalline molecular machines, samples 1,4-bis(iodoethynyl)bicyclo[2.2.2]octane (BIBCO) were synthesized crystallized. Knowing that are common between electron-rich acetylenic carbons electron-deficient iodines, it was expected BIBCO rotors would be an ideal platform formation array rotors. Variable temperature single crystal X-ray crystallography established presence halogen-bonded network, characterized by lamellarly ordered layers crystallographically unique rotors, which undergo reversible monoclinic-to-triclinic phase transition at 110 K. In order elucidate rotational frequencies activation parameters variable-temperature 1H wide-line 13C cross-polarization/magic-angle spinning solid-state NMR experiments performed temperatures 27 290 Analysis spin−lattice relaxation second moment as function revealed two dynamic processes simultaneously present over entire range studied, with temperature-dependent rates krot = 5.21 × 1010 s−1·exp(−1.48 kcal·mol−1/RT) 8.00 s−1·exp(−2.75 kcal·mol−1/RT). Impressively, these correspond room 4.3 0.8 GHz, respectively. Notably, high-temperature plastic I bicyclo[2.2.2]octane has reported energy 1.84 kcal·mol−1 for rotation about 1,4 axis, is 24% larger than Ea 1.48 same motion fastest rotor; yet, rotor three fewer degrees translational freedom freedom! Even more so, represent some engineered date. The results this study highlight halogen bonding valuable tool design synthesis amphidynamic artificial machines suggest modulating properties depend on dielectric behavior media.