Synthesis, Characterization, and Magnetic Studies of Coordination Polymers with Co(II) and Mn(II) Ions

An ether bridged tricarboxylic acid ligand, 5-(4-carboxybenzyloxy)isophthalic acid (p-cbiaH(3)) has been used to construct three coordination polymers with Co(II) salts in presence of different nitrogen donor ligands such as 1,4-bis(4-pyridinylmethyl)piperazine (bpmp), dipyridine-4-yl-diazene (dpd), and 4,4'-bipyridine (bpy). The products formed under hydrothermal conditions are formulated as {[Co-3(p-cbia)(2)(bpmp)(2)(H2O)(6)]center dot 10H(2)O}(n) (1), {[Co-2(p-cbiaH)(2)(dpd)(H2O)(2)]}(n) (2) and {[Co-3(p-cbia)(2)(bpy)(H2O)(8)]center dot 6H(2)O}(n) (3). Reacting with MnCl2 center dot 4H(2)O under solvotherrnal condition, it affords {[Mn-3(p-cbia)(2)(DMF)(2)]center dot DMF}(n) (4). All the complexes have been characterized by single-crystal X-ray diffraction, IR spectroscopy, thermogravimetry, elemental analysis, and powder X-ray diffraction (PXRD) measurements. Topological analysis reveals that 1 is a (3,4)-connected jeb net, 2 is a (3,8)-connected tfz-d net, while 3 forms a 3-connected hcb type net. However, with the Mn(II) salt, it forms a 3D coordination polymer with a novel (5,6,6)-connected, three nodal net with novel pkb-4 topology. Magnetic susceptibility measurements of complexes 1, 2, and 4 were carried out in the temperature range 2-300 K. Complex 1 exhibits weak ferromagnetic ordering at low temperature owing to the frustration of one of the Co(II) ions in the unit cell. Complex 2 shows a peak at similar to 6.1 K in ZFC susceptibility, which might result from weak ferromagnetic interactions between carboxylate-bridged Co(II) ions. Complex 4 shows a signature of antiferromagnetic behavior followed by weak ferromagnetic interactions at low temperature.