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

Abstract

The reaction of [Co 2 (H 2 O)(TFMBz) 4 (py) 4 ] (1) (TFMBz: 3,5bis(trifluoromethyl)benzoate; 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 CO 2 (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 carboxylate 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.