Two novel 2D cadmium(ii) MOFs based on flexible bis(imidazolyl) and zwitterionic dicarboxylate ligands

Abstract

The reaction of 1,4-bis((pyridinium-4-carboxylic acid)methyl)benzene dibromide (Bpmb-2HBr), Cd(NO₃)₂·4H₂O with 1,2-bis(imidazol-1′-yl)ethane (Bime) and 1,4-bis(imidazol-1′-yl)butane (Bimb) gave rise to two novel 2D Cd(II) coordination polymers, [Cd_1.5(Bime)(Bpmb)_0.5(μ-Br)Br₂·DMF]_n (1) and [Cd₂(Bimb)₂(μ-Br)₂Br₂]_n (2), respectively, in which coordination of μ-Br⁻ and monodentate Br⁻ with Cd(II) generates an unprecedented trimeric [Cd₃(μ-Br)₂Br₄] unit in 1 and a dimeric [Cd₂(μ-Br)₂Br₂] unit in 2. In 1, gauche-Bime links the central six-coordinated Cd(II) of the trimers into a 1D double chain, anti-Bpmb further bridges the terminal four-coordinated Cd(II) of the trimers in the opposite direction to generate a 2D layer. Complex 2 is a 2D corrugated layer consisting of perpendicular left- and right-handed helical chains constructed through anti-anti-gauche-conformated Bimb bridging the neighboring six-coordinated Cd(II) of [Cd₂(μ-Br)₂Br₂] units. The thermal stability and fluorescent properties of the two complexes have also been studied.