Guest-Responsive Reversal in Structural Transformation after a [2 + 2] Topochemical Reaction in a 3D Pillared Layer MOF: Uncovering the Role of C-H···O Interaction.

Here, we report the influences of the C-H···O interaction, weaker than other conventional noncovalent interactions, on the guest-responsive structural modification of a photoactive metal-organic framework (MOF) and the impact on gas sorption properties. A photoactive pillared-layer three-dimensional MOF {[Cd(pzdc)(bpee)]·3HO} () (where bpee = 1,2-bis(4-pyridyl)ethylene and pzdc = 2,3-pyrazinedicarboxylate) was synthesized and characterized. Compound shows guest-responsive structural contraction by the movement of two-dimensional layers supported by the C-H···O interaction between the pillar (bpee) and layer (pzdc) linkers. Further, was postsynthetically modified using light by exploiting the parallel arrangement of the olefinic double bondsof the bpee pillars based on a [2 + 2] cycloaddition reaction to produce {[Cd(pzdc)(-tpcb)]·3HO}, () (-tpcb = -tetrakis(4-pyridyl)cyclobutane) in a single-crystal-to-single-crystal transformation (SCSC) manner. The C-H···O interaction between the two linkers is not possible in the photomodified framework, and thus guest-responsive structural expansion is realized. Such a reversal of the structural transformation facilitates the enhanced CO uptake in with respect to at their dehydrated states. Further, the photomodified compound does not uptake N and CH at 273 K and shows high selectivity as realized by an ideal adsorbed solution theory calculation. The facile diffusion of CO in the irradiated framework is also supported by the kinetic measurements based on MeOH adsorption isotherms at 293 K. Here, postsynthetic modification by a [2 + 2] photochemical reaction is the key to control the structural change for enhanced CO uptake capacity.