Abstract
Porous metal complexes such as metal-organic framework (MOF) and porous coordination polymer (PCP) are one of the current attractive structural motifs because of their utility for several practical applications such as storage and separation of ions/molecules, catalysis, and proton conduction. Herein, this paper focuses on coordinatively unsaturated sites arranged in porous metal complexes as useful function centers. For example, unsaturated sites of Cu(II) and Zn(II) in two porous metal complexes, Cu3(btc)2 (btc = 1,3,5-benzenetricarboxylate) and Zn2(dobdc) (dobdc = 2,5-dioxido-1,4-benzenedicarboxylate), respectively, serves as good binding sites for hydrogen molecules as proven by neutron powder diffraction. Similar ferrous MOF, Fe2(dobdc), also realized the separation of olefin and paraffin gases through strong interaction between olefin molecules and the unsaturated Fe(II) sites. Furthermore, it was found that the unsaturated sites of Fe2(dobdc) could bind oxygen molecules through redox reaction to generate Fe(II/III)-O2- or Fe(III)-O22- species depending on the temperature. Therefore, application of the unsaturated coordination sites of MOF/PCP is promising not only for gas storage, separation and catalysis but also for a field of bioinorganic chemistry as active site models of metalloenzymes.
