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-cbiaH3) 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 {[Co3(p-cbia)2(bpmp)2(H2O)6]·10H2O}n (1), {[Co2(p-cbiaH)2(dpd)­(H2O)2]}n (2) and {[Co3(p-cbia)2(bpy)­(H2O)8]·6H2O}n (3). Reacting
with MnCl2·4H2O under solvothermal condition,
it affords {[Mn3(p-cbia)2(DMF)2]·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 ∼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.