Structures and photoluminescence properties of two cadmium(II) coordination polymers synthesized by flexible and rigid ligands

摘要

Two new Cd(II) coordination polymers, [Cd(BDC)(m-bitmb)(H_2O)] (1) and [Cd_2(BDC)_2(p-bitmb)_(1.5)(H_2O)_2] (2), have been solvothermally synthesized by reacting cadmium sulfate and 1,4-benzenedicarboxylic acid (H_2BDC) with flexible ligands 1,3-bis(1-imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (m-bitmb) or 1,4- bis(1-imidazol-1-ylmethyl)-2,3,5,6-tetramethylbenzene (p-bitmb), respectively. Compound 1 shows an uncommon 3D 4-connected 6~6 topology, a distorted diamond structure, while compound 2 is a novel 2D (3,4)-connected W-shape-like layer framework with a novel (6~3?6~6) topology. 1 and 2 have different fluorescence and thermal properties. Compound 1 shows a ligand based fluorescence, while compound 2 shows a red-shifted emission compared to the ligands and is assigned to the ligand-to-ligand charge transfer (LLCT) emission. These results demonstrated the structure-property relationship of MOF material.