Synthesis, structure and thermodynamics/kinetics analysis of three different interpenetrating zinc(II) coordination architectures

Abstract

Based on flexible 1,4-bis(2-methyl-imidazol-1-yl)butane (bib) and three rigid line-shaped carboxylate mix-ligands, three Zn(II) coordination polymers, {[Zn2(bib)2(1,4-ndc)2]·H2O}n (1), {[Zn0.5(bib)0.5(bdc-Br2)0.5]·0.5H2O}n (2), {[Zn2(bib)(4,4'-bpdc)2] · H2O}n (3)(1,4-H2ndc = 1,4-naphthalenedicarboxylic acid, H2bdc-Br2 = 2,5-dibromoterephthalic acid, 4,4'-H2bpdc = 4,4'-biphenyldicarboxylic acid) have been synthesized under solvothermal conditions and characterized by elemental analysis, infrared (IR) spectrometry, and single crystal X-ray diffraction. 1 presents a 4-fold interpenetrating framework including three kinds of zigzag chains. 2 exhibits an unusual [2 + 2] interpenetrating framework. 3 features a 3-fold interpenetrating network. Their thermal decomposition behaviors were investigated by simultaneous thermogravimetry/differential thermal gravity and differential scanning calorimetry (TG/DTG-DSC) techniques. The TG curves indicate that the unusual [2 + 2] interpenetrating framework exhibits the highest thermal stability of the three frameworks, and the 4-fold interpenetrating framework exhibits higher thermal stability than the 3-fold interpenetrating framework. The thermodynamics and kinetics of skeleton collapse for the complexes were calculated by the integral Kissinger's method and Ozawa-Doyle's method. The activation energies (E) of 276.887, 318.515, and 149.310 kJ·mol-1 illustrate the relationship of the reaction rates of complexes 1-3: 3 > 1 > 2. The structural characteristics could be elucidated from the thermodynamics and kinetics. Moreover, the fluorescent properties of complexes 1-3 were also studied.