Syntheses, structures, luminescence and magnetic properties of seven isomorphous metal–organic frameworks based on 2,7-bis(4-benzoic acid)-N-(4-benzoic acid)carbazole

Abstract

We report herein seven novel lanthanide metal–organic frameworks (Ln-MOFs), [M(L₂₇)(DMA)(H₂O)·XH₂O]_n (TCZ-M), (M = Nd, Sm, Eu, Gd, Tb, Dy, Ho), (X = 2 or 3) (H₃L₂₇ = 2,7-bis(4-benzoic acid)-N-(4-benzoic acid)carbazole, DMA = N,N-dimethylacetamide, TCZ = “T”-shape carbazole-based MOFs, L₂₇ = fully deprotonated H₃L₂₇³⁻ ligand). X-ray crystallography showed that all the TCZ-M (M = Nd, Sm, Eu, Gd, Tb, Dy, Ho) are isomorphous and possess a 3,6-connected three-dimensional (3D) framework with a point symbol of {4·6²}₂{4²·6¹⁰·8³}. The photoluminescence measurement indicates that TCZ-Eu shows reddish-orange emission bands and TCZ-Sm shows both visible and near-infrared (NIR) emission bands. Magnetic susceptibility measurements show deviations from the Curie law mainly owing to the split of the ground term due to the ligand field and spin–orbit coupling in TCZ-Eu and TCZ-Sm. The magnetic properties of TCZ-M (M = Nd, Gd, Tb, Dy, Ho) are also investigated, and the results indicate a ferromagnetic interaction between the Tb³⁺ magnetic centers in TCZ-Tb and the antiferromagnetic interactions in TCZ-M (M = Nd, Gd, Dy, Ho).