Three isomorphous porous metal-organic frameworks (MOFs; PCN-9 (Co/Fe/Mn)) with entatic metal centers have been constructed on the basis of the trigonal planar H(3)TATB ligand and a novel square-planar secondary building unit. N(2) adsorption isotherms at 77 K confirmed the permanent porosities of the three porous MOFs. Variable-temperature adsorption measurements of H(2) revealed that the H(2) affinities of the three porous MOFs are related to the nature of entatic metal centers, which reversely affect their H(2) uptake capacities.