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-cbiaH3), 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, {[Co4(OH)2(p-cbia)2(bpmp)-(H2O)3]·2H2O}n (1) and {[Co4(OH)2(p-cbia)2(dpe)­(H2O)4]·2H2O}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 [Co4(μ3-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.