Coordination polymers of the conformation-flexible 1,2,4,5-cyclohexanetetracarboxylate: synthesis, structures and transforming mechanism studies

Abstract

Four new cobalt coordination polymers based on cyclohexane-1e,2a,4a,5e-tetracarboxylic acid (2e+2a, H₄L^I), [Co₄(μ₄-L^I)₂(4,4′-bpy)₃(H₂O)₆]·2H₂O (1), [Co₄(μ₅-L^I)₂(4,4′-bpy)₃(H₂O)₄]·3H₂O (2), [Co₂(μ₄-L^IV)(2,2′-bpy)₂(H₂O)₂] (3) and [Co₂(μ₄-L^IV)(1,10-phen)₂(H₂O)₂]·4H₂O (4), were synthesized in hydrothermal reactions with some auxiliary ligands to study the conformations and coordination chemistry of H₄L. The structural analysis revealed a new conformation, cyclohexane-1e,2e,4e,5e-tetracarboxylic acid (4e, H₄L^IV), for the flexible ligand H₄L trapped in compounds 3 and 4, which were synthesized in the presence of different chelating ligands whereas in the compounds of 1 and 2, the ligands adapt the same conformation (2e+2a, H₄L^I) as found in the solid state when the linear bridging 4,4′-bpy was added as auxiliary ligand. The conformational transformation originated from the removal of α-protons of H₄L, which has been confirmed via the production of [Cu^I(4,4′-bpy)(H₂O)]₂(ip)·2H₂O (5) (H₂ip = isophthalic acid) from the reaction of Cu²⁺ ions, H₄L^I ligand and 4,4′-bpy under hydrothermal conditions. The magnetic properties of 2 and 3 were investigated‥