Polymorphic Ln(III) and BPTC-based porous metal-organic frameworks with visible, NIR photoluminescent and magnetic properties

By reaction of 3,3 ',5,5 '-biphenyltetracarboxylic acid (H4BPTC) with various lanthanide ions, seven novel three dimensional (3D) lanthanide metal-organic frameworks (MOFs) have been prepared under solvothermal conditions, namely, [Ln(3)(BPTC)(3)(H2O)2]center dot 3H(3)O center dot 4H(2)O center dot 3DMF (DMF = N, N-dimethylformamide, Ln = Eu (1), Tb (2), Sm (3) Dy (4)), [Nd(BPTC)(H2O)2]center dot H3O center dot DMF (5), [Er-2(BPTC)(HCOO)(3)(H2O)(2)]center dot(CH3)(2)NH2 (6), and [Tm-12(BPTC)(8)(HCOO)(11)(H2O)(10)]center dot 10DMF center dot 7(CH3)(2)NH2 (7). Combining different lanthanide ions and diversity of coordination modes of the H4BPTC ligand, the seven compounds display interesting structural characteristics. Of these, compounds 1- 4 are isostructural and demonstrate a unique 3D coordination framework containing two types of 1D channel, that is built by the novel trinuclear [Ln(3)O(22)] SBUs. Compound 5 can be described as a new 3D open-framework structure with quadrilateral-shaped 1D channels based on [Nd2O16] SBUs. Compound 6 has a new 3D pillar network feature constructed by trapezoidal chains linked by bridging BPTC4- ligands, whilst compound 7 exhibits a 3D network with a number of rare oval-shaped channels along the [101] direction. The H4BPTC ligand exhibits five new coordination modes, which are firstly reported in M-BPTC frameworks. Compounds 1- 7 all display their typical emission bands upon irradiation at the ligand band at room temperature. Compounds 1- 4 present strong characteristic emissions in the visible region, of which compounds 1 and 2 show millisecond luminescence lifetimes. The NIR photoluminescent of lanthanide MOFs is less well observed, especially for the Tm(III) compounds. Owing to the good sensitization of the H4BPTC ligand, compounds 5-7 display near-infrared region (NIR) emission with microsecond luminescence lifetimes. In addition, compounds 2, 5, 6 and 7 exhibit global antiferromagnetic behaviors, of which compound 5 shows a weak ferromagnetic coupling at 235 K.