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) {[V(OH)(L)], LH=biphenyl-3,3',5,5'-tetracarboxylic acid} can be oxidized to isostructural MFM-300(V), [VO(L)], in which deprotonation of the bridging hydroxyl groups occurs. MFM-300(V) shows the second highest CO uptake capacity in metal-organic framework materials at 298 K and 1 bar (6.0 mmol g) and involves hydrogen bonding between the OH group of the host and the O-donor of CO, which binds in an end-on manner, =1.863(1) Å. In contrast, CO-loaded MFM-300(V) shows CO bound side-on to the oxy group and sandwiched between two phenyl groups involving a unique ···c.g. interaction [3.069(2), 3.146(3) Å]. The macroscopic packing of CO in the pores is directly influenced by these primary binding sites.