Syntheses, Crystal Structures, and Magnetic Properties of Metal–Organic Hybrid Materials of Co(II) Using Flexible and Rigid Nitrogen-Based Ditopic Ligands as Spacers

A carboxylate-based flexible ligand, 5-(4-carboxybenzyloxy)isophthalic acid ( p -cbiaH 3 ), readily reacts with Co(II) salts in the presence of different pyridine-based coligands such as 4-bis(4-pyridinylmethyl)piperazine (bpmp) or 1,2-di(4-pyridyl)ethylene (dpe) under hydrothermal conditions to afford two different three-dimensional (3D) coordination polymers, {[Co 4 (OH) 2 ( p -cbia) 2 (bpmp)-(H 2 O) 3 ]·2H 2 O} n ( 1 ) and {[Co 4 (OH) 2 ( p -cbia) 2 (dpe)(H 2 O) 4 ]·2H 2 O} n ( 2 ). Both compounds have been characterized by X-ray crystallography, IR spectroscopy, thermogravimetry, and elemental analysis. Single-crystal X-ray diffraction studies reveal that both compounds consist of a tetranuclear core [Co 4 (μ 3 -OH) 2 ] 6+ . Compound 1 is a unprecedented 3D non-interpenetrated (3,4,9)-connected pkb3 net. On the other hand, compound 2 is a 2-fold interpenetrated (3,8)-connected tfz-d net. Variable temperature static and dynamic magnetic measurements show that both compounds exhibit ferromagnetic behavior associated with mixed hydroxyl/carboxylate-bridged tetranuclear Co(II) clusters as subunits.