Metal−Organic Framework Isomers with Diamondoid Networks Constructed of a Semirigid Tetrahedral Linker

Solvothermal assembly of a semirigid tetrahedral carboxylate ligand tetrakis[4-(carboxyphenyl)oxamethyl]methane acid (H4X) with Cd(II) ion in different solvent systems yields three novel metal−organic framework isomers (1−3) based on different secondary building units (SBUs). Although all three frameworks have the same dia (diamondoid) topology, complexes 1 and 3 are noncentrosymmetric and complex 2 is centrosymmetric. One of the networks (1) shows cross-linked 3-fold interpenetration of the single dia net and exhibits permanent porosities, as confirmed by Brunauer−Emmett−Teller (BET) and selective CO2 adsorption.