Supramolecular Isomerism in Cobalt(II) Coordination Polymers Built from 3,5-Bis(trifluoromethyl)benzoate and 4,4′-Bipyridine

The reaction of [Co-2(H2O)(TFMBz)(4)(py)(4)] (1) (TFMBz: 3,5-bis(trifluoromethyl)Obenzoate; py: pyridine) with 4,4'-bipyridine (bpy) in different solvents yields four coordination polymers with unlikely structures but with the same stoichiometry. Three of them contain similar ladder chains consisting of binuclear nodes "Co-2(TFMBz)(4)", in which two of the TFMBz ligands show bidentate bridge coordination, double linked to each adjacent node by bpy but packed in different fashions. The different packing affects the compound porosity; thus, [Co-2(TFMBz)(4)(bpy)(2)](n) (2), precipitated using low-polarity solvents such as supercritical CO2 (scCO(2)), n-butyl acetate, or heptane and also in acetonitrile, is microporous, with a surface area of 330 m(2)g(-1), showing the N-2 adsorption/desorption isotherm at 77 K with a gate-opening effect at low relative pressures (P/P-0 = 0.05). The isomer [Co-2(TFMBz)(4)(bpy)(2)](n) (3), synthesized in ethoxyethanol, presents a surface area of 230 m(2)g(-1). A third chain packing isomer, [Co-2(TFMBz)(4)(bpy)(2)](n) (4), is obtained in acetone and has only non-interconnected voids. Finally, precursor 1 is combined with bpy in a highly polar solvent such as water to give [Co(TFMBz)(2)(bpy)](n) (5). In this isomer, all the carbozylate units act as bidentate bridging ligands, generating chains that are interlinked by bpy, leading to a 2D network, which after packing yields a non-porous structure. The resolution of structures 2-5 is only possible with the recently developed 3D electron diffraction method based on the collection of diffraction patterns on sub-micron-sized single crystals. The variation of magnetic susceptibility as a function of temperature is also measured. Overall, our work provides insightful information on the complex landscape of metal-organic framework solids that are formed by crystallization using different solvent media.