Cooperative Bond Scission in a Soft Porous Crystal Enables Discriminatory Gate Opening for Ethylene over Ethane

Here
we report a soft porous crystal possessing hemilabile cross-links
in its framework that exhibits exclusive gate opening for ethylene,
enabling the discriminatory adsorption of ethylene over ethane. A
Co-based porous coordination polymer (PCP) bearing vinylogous tetrathiafulvalene
(VTTF) ligands, [Co­(VTTF)], forms Co–S bonds as intermolecular
cross-links in its framework in the evacuated closed state. The PCP
recognizes ethylene via d−π complexation on the accessible
metal site that displaces and cleaves the Co–S bond to “unlock”
the closed structure. This ethylene-triggered unlocking event facilitates
remarkable nonporous-to-porous transformations that open up accessible
void space. This structural transformation follows a two-step gate-opening
process. Each phase, including the intermediate structure, was successfully
characterized by single-crystal X-ray diffraction analysis, which
revealed an intriguing “half-open” structure suggestive
of a disproportionate gate-opening phenomenon. The gate-opening mechanism
was also investigated theoretically; density functional theory and
Monte Carlo calculations revealed that the unique “half-open”
phase corresponds to a substantially stable intermediate over the
possible transformation trajectories. While ethylene opens the gate,
ethane does not because it is unable to coordinate to the Co center.
This feature is maintained even at pressures above 1 MPa and at a
temperature of 303 K, demonstrating the potential of the “gate-locking/unlocking”
mechanism that exploits the hemilabile cross-linking in soft porous
crystals.