Three-dimensional pillared metallomacrocycle-graphene frameworks with tunable micro- and mesoporosity

We report on a new class of hierarchical micro- and mesoporous materials, termed metallomacrocycle-graphene frameworks (MGFs), which can be constructed by covalently and/or coordinatively pillaring graphene oxide (GO) sheets with metallomacrocycles. This approach to fabricating 3D MGFs enables the alternative stacking of GO and Ni(ii/iii) metallomacrocycles in a layer-by-layer manner, without phase separation of the structural entities. We show that, depending on the preparation conditions, the porosity of the MGFs could be modulated from microporous to hierarchical micro- and mesoporous, and concomitantly, the oxidation states of the Ni centers within the pillars could be changed. These intriguing features of the MGFs allowed the usually unstable square planar Ni(iii) species to be stabilized in the solid state, thus providing highly active Lewis acidic sites for foreign reactants. The physically and chemically modulated nanoporous MGFs exhibited extremely high H₂ storage capacities as well as interesting electrocatalytic activity towards oxygen reduction reactions in an alkaline medium. We believe that the design strategy exploited for these MGFs could be further extended to a variety of 3D porous graphene-based nanoarchitectured materials.