Synthesis, crystal structures, adsorption and fluorescence properties of coordination polymers based on a semirigid octadentate ligand

Abstract

Using an octadentate ligand, namely tetrakis[(3,5-dicarboxyphenoxy)methyl] methane (H8L), four coordination polymers, [Ni3L(OH)2(H2O)2][NH2(CH3)2]4·5H2O (1), [Co4L(H2O)4]·9H2O (2), [Zn4L(H2O)4]·DMF·11H2O (3) and [Li4(H4L)(H2O)4] (4) (DMF = N,N-dimethylformamide), have been solvothermally synthesized and structurally characterized by X-ray crystallography. Complex 1 is an anionic three-dimensional open framework built from tricluster {Ni3(COOR)8} and square planar L ligands to give a uninodal 6-connected pcu network. Complexes 2 and 3 are isostructural, possessing a non-interpenetrated three-dimensional network with rare (4,8)-connected scu topology. Complex 4 consists of 4-connecting {Li2(COOR)4} clusters which form a 2D Shubnikov tetragonal plane net with sql topology. Complexes 1–3 all have large solvent accessible voids, but only complex 3 possesses permanent porosity as confirmed by N2, H2, CO2 and CH4 gas adsorption measurements. In addition, complex 3 shows strong photoluminescent emissions at room temperature with a peak at 365 nm, owing to a ligand-centered excited state. The emission intensities of 3 varied upon contact with different solvents or analytes.