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Porous lithium imidazolate frameworks constructed with charge-complementary ligands.

Metal-organic frameworks (MOFs) based on 4-connected nodes are of special interest because of their zeolite-like topologies and open architectures.[1–2] A fundamental structural feature of zeolite topology is tetrahedral nodes (e.g., Si4+) crosslinked by a bicoordinated bridge (e.g., O2− as in SiO2). This bonding feature can be emulated by metal cations (or clusters) and organic crosslinking ligands. Until now, several metallic elements (e.g., Zn, Cd, and In) have been found to generate zeolite-like MOFs including zeolitic imidazolate frameworks (ZIFs) and indium-based ZMOFs.[3–6] The replacement of these transition (or post-transition) metals with lightweight main group metals (e.g., Li, Mg, and Al) has potential to produce a lower framework density, which is desirable for enhancing gravimetric energy storage capacity of gas storage materials. In the past several years, the synthesis of MOFs based on lightweight metals has attracted much attention with the greatest successes being achieved in Mg- and Al-MOFs.[7–8] Nevertheless, to date, the framework based on only 4-connected lithium nodes remains unknown, even though Li-containing boron imidazolate frameworks and frameworks containing Li-O clusters or chains are known.[9]