Porous Anionic, Cationic, and Neutral Metal-Carboxylate Frameworks Constructed from Flexible Tetrapodal Ligands: Syntheses, Structures, Ion-Exchanges, and Magnetic Properties

A series of coordination polymers with anionic, cationic, and neutral metal-carboxylate frameworks have been synthesized by using a flexible tetrapodal ligand tetrakis[4-(carboxyphenyl)oxamethyl] methane acid (H4X). The reactions between divalent transition-metal ions and H4X ligands gave [M3X2]·[NH2(CH3)2]2·8DMA (M = Co (1), Mn (2), Cd(3)) which have anionic metal-carboxylate frameworks with NH2(CH3)2+ cations filled in channels. The reactions of trivalent metal ions Y(III), Dy(III), and In(III) with H4X ligands afforded cationic metal-carboxylate frameworks [M3X2·(NO3)·(DMA)2·(H2O)]·5DMA·2H2O (M = Y(4), Dy(5)) and [In2X·(OH)2]·3DMA·6H2O (6) with the NO3− and OH− serving as counterions, respectively. Moreover, a neutral metal-carboxylate framework [Pb2X·(DMA)2]·2DMA (7) can also be isolated from reaction of Pb(II) and H4X ligands. The charged metal-carboxylate frameworks 1−5 have selectivity for specific counterions in the reaction system, and compounds 1 and 2 display ion-exchange behavior. Moreover, magnetic property measurements on compounds 1, 2, and 5 indicate that there exists weak antiferromagnetic interactions between magnetic centers in the three compounds.