Modulating supramolecular binding of carbon dioxide in a redox-active porous metal-organic framework

Hydrogen bonds dominate many chemical and biological processes, and chemical modification enables control and modulation of host-guest systems. Here we report a targeted modification of hydrogen bonding and its effect on guest binding in redox-active materials. MFM-300(V-III) {[V-III (2)(OH)(2)( L)], LH4 = biphenyl-3,3',5,5' -tetracarboxylic acid} can be oxidized to isostructural MFM-300(V-IV), [(V2O2)-O-IV(L)], in which deprotonation of the bridging hydroxyl groups occurs. MFM-300(V-III) shows the second highest CO2 uptake capacity in metal-organic framework materials at 298 K and 1 bar (6.0 mmol g(-1)) and involves hydrogen bonding between the OH group of the host and the O-donor of CO2, which binds in an end-on manner, OH center dot center dot center dot O-CO2 = 1.863(1)angstrom. In contrast, CO2- loaded MFM- 300(V-IV) shows CO2 bound side-on to the oxy group and sandwiched between two phenyl groups involving a unique O-CO2 center dot center dot center dot c. g(.phenyl) interaction [3.069(2), 3.146(3) angstrom]. The macroscopic packing of CO2 in the pores is directly influenced by these primary binding sites.