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

A series of interesting Co(II)-H(2)tbip coordination polymers incorporating different auxiliary ligands, {[Co(tbip)(bipy)(H2O)(3)]center dot 0.5(bipy)center dot H2O}(n) (1), [Co(tbip)(bipy)](n)(2), {[Co-3(tbip)(3)(dpe)(3)]center dot 0.5(dpe)center dot 3H(2)O}(n) (3), [Co-2(tbip)(2)(dpe)(H2O)](n) (4), [Co-2(tbip)(2)(bpa)(H2O)](n) (5), and {[Co-2(tbip)(2)(bpa)(2)]center dot 2.5H(2)O}(n) (6) (H(2)tbip = 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 1 D zigzag bipy-bridged polymeric chains with the terminal tbip ligands as pendants, which are extended to a 3D hydrogen-bonded supramolecular framework involving 1 D 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 4(8).6(6).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 alpha-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.