An insight into the controllable synthesis of Cd(II) coordination polymers with packing-assistant luminescent property

Abstract

Three luminescent materials, {[Cd(m-bix)(2,5-tdad)]·H2O}n(1), [Cd(m-bix)(1,4-bda) (H2O]n(2), [Cd(m-bix)(Cl)2]n(3) [m-bix = 1,3-bis-(imidazol-1-ylmethyl) benzene, 2,5-H2tdad = 2,5-thiophenedicarboxylic acid; 1,4-H2bda = 1,4-benzenedicarboxylic acid] have been hydrothermally synthesized by mixed ligands and characterized by single crystal X-ray diffraction, infrared (IR), elemental analysis and thermogravimetric analysis (TGA). Single-crystal X-ray diffraction analysis reveals that 1–3 exhibit three different structural types: 1 displays a wavelike 2D structure constructed from [CdO5N2] clusters with the help of 2,5-H2tdad. 2 is defined as a 3D supramolecular structure based on π⋯π stacking interactions. Both 1 and 2 display remarkable alternate π⋯π stacking interactions, providing the effective distance for transmission of MLCT. 3 can be regarded as a 6-connected pcu net with the Schläfli symbol {412·63}, featuring binuclear [Cd2Cl6N4] Cl-bridge clusters. Coordination polymers 1–3 display tunable luminescence from deep blue, blue, light blue to green with the red-shift at 298 K and 77 K. 3 displays remarkable narrow band emission with a smaller full width at half-maximum (FWHM) (77 K: 46.98 nm; 298 K: 72.63 nm) in the solid state, which endows the excellent monochromaticity. The mechanism of fluorescence has been explained and verified by density functional theory (DFT) calculations.