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.