Self-Assembly of a Series of Cobalt(II) Coordination Polymers Constructed from H₂tbip and Dipyridyl-Based Ligands

A series of interesting Co(II)−H2tbip coordination polymers incorporating different auxiliary ligands, {[Co(tbip)(bipy)(H2O)3]·0.5(bipy)·H2O}n (1), [Co(tbip)(bipy)]n (2), {[Co3(tbip)3(dpe)3]·0.5(dpe)·3H2O}n (3), [Co2(tbip)2(dpe)(H2O)]n (4), [Co2(tbip)2(bpa)(H2O)]n (5), and {[Co2(tbip)2(bpa)2]·2.5H2O}n (6) (H2tbip = 5-tert-butyl isophthalic acid; bipy = 4,4′-bipyridine; dpe = 1,2-di (4-pyridyl)ethylene; bpa = 1,2-bi(4-pyridyl)ethane) were synthesized. X-ray structural analyses of 1−6 reveal a diverse range of structures, ranging from 1D (1) to 2D (2, 6) to 3D (3, 4, 5). Complex 1 shows 1D zigzag bipy-bridged polymeric chains with the terminal tbip ligands as pendants, which are extended to a 3D hydrogen-bonded supramolecular framework involving 1D open channels which encapsulate guest bipy molecules. Polymers 2 and 6 feature similar 2D infinite layer frameworks consisting of cobalt dimers. The structure of 3 is constructed from [Co2(tbip)2]n layers, which consists of alternating left- and right-handed helical chains, and further pillared by dpe ligands into a 3D six-connected self-penetrating 48.66.8 network. The prominent cavities in 3 are parallel to the (101) plane and encapsulate free dpe as guest molecules. Polymers 4 and 5 are isostructural, showing 2-fold interpenetrating 3D α-Po networks constructed from binuclear cobalt nodes. The thermal stabilities and X-ray powder diffraction studies indicate that the framework of 3 can keep stable after the loss of guest molecules. Studies of the magnetic susceptibilities of 2−6 reveal weak antiferromagnetic exchange interactions between adjacent Co(II) centers.