Synthesis, Structure, and Magnetic Properties of Cobalt(II) Coordination Polymers from a New Tripodal Carboxylate Ligand: Weak Ferromagnetism and Metamagnetism

A new tripodal carboxylic ligand, 5-(4-carboxy-phenoxy)-isophthalic acid, readily (cpiaH 3 ) reacts with Co(II) salts in the presence of pyridine-based coligands under solvothermal conditions to afford four different coordination polymers, {Co 2 (cpia)(OH)(bipy) 0.5 } n ( 1 ), {[Co 2 (cpia)(OH)(H 2 O) 2 ]·H 2 O} n ( 2 ), {Co 1.5 (cpia)(bipyethane)} n ( 3 ), and {Co 1.5 (cpia)(pyridine) 2 } n ( 4 ). All these coordination polymers have been characterized by single crystal X-ray diffraction, IR spectroscopy, thermogravimetry and elemental analysis. The structures of 1 and 2 can be described as a repetition of a tetranuclear core with subtle differences — two tetranuclear cores are shared by an O atom in 2, while no such bridging is present in 1 . The structures of 3 and 4, on the other hand, consist of a trinuclear core extending to three-dimensional networks. Variable temperature magnetic susceptibility measurements indicate that 1 exhibits ferromagnetic behavior below 13 K, while 2 shows metamagnetic behavior. These interesting magnetic features are associated with the mixed hydroxyl/carboxylate-bridged polynuclear Co(II) clusters as subunits.