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

Article abstract of DOI:10.1039/c7nj04048b

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 H₃L₂₇^3- 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).