The influence of 1-alkyl-3-methyl imidazolium ionic liquids on a series of cobalt-1,4-benzenedicarboxylate metal–organic frameworks

Abstract

To investigate the influence of ionic liquids on the structures and properties of the complexes, ionothermal synthesis of 1,4-benzenedicarboxylate acid (H₂BDC) reacting with Co(NO₃)₂ with four different 1-alkyl-3-methylimidazolium bromides produced three layered metal–organic frameworks with the chemical formula [RMI]₂[Co₃(BDC)₃Br₂], (R = ethyl for 1; n-propyl for 2, and n-butyl for 3; MI = imidazolium) and a 3D architecture [AMI]₂[Co₃(BDC)₄] (4) (A = amyl). Compounds 1–3 have the same (3,6) skeleton with [RMI]⁺ cations located in the interlayer space. Compound 4 grows into a 3D architecture based on BDC²⁻ ligands linking similar 2D grids as those in 1–3. The [RMI]⁺ templates exert their influence on the diagonal sizes of the quadrilateral grids, the interlamellar spacing, and the solvent-accessible cavities through steric hindrance. By comparison of 1–3, the [RMI]⁺ templates also have an effect on the properties. As the alkyl chains in [RMI]⁺ increase, the decomposing temperatures increase, emission peaks around 400 nm blue shift, and the cavities of 1–3 decrease. 1–3 exhibit ferromagnetism with similar magnetic parameters, while 4 reveals antiferromagnetism.