Synthesis, structure, photoluminescent and thermodynamic/kinetic properties of two interpenetration/polycatenation Zn(II) coordination polymers

Two novel zinc(II) coordination polymers, [Zn2(bib)(5-Br-ipa)2]}n (1) and {[Zn(bib)(2,6-ndc)]}n (2) (bib = 1,4-bis(2-methyl-imidazol-1-yl)butane, 5-Br-H2ipa = 5-bromoisophthalic acid, 2,6-H2ndc = 2,6-naphthalenedicarboxylic acid) have been synthesized under the same solvothermal conditions and characterized by elemental analysis, IR spectroscopy, single crystal X-ray diffraction technology. Complex 1 shows a novel 3-fold interpenetrating architecture possessing a couple of single helices and a pair of rare tri-flexural helices. Complex 2 gives an unusual 2D + 2D → 3D inclined polycatenation architecture comprised of two sets of interlocked equivalent 2D layers. The fluorescent properties of complexes 1 and 2 were studied. In addition, the thermal decompositions of 1 and 2 were investigated by simultaneous TG/DTG–DSC techniques. The TG curves exhibit that complexes 1 and 2 possess good thermostability up to 320 °C and 315 °C, respectively. The enthalpy of the melting decomposition (ΔHd) was measured. The apparent activation energy E and the pre-exponential factor (A) of skeleton collapse for the complexes were calculated by the integral Kissinger’s method and Ozawa–Doyle’s method. The thermodynamic parameters (ΔH≠, ΔG≠, and ΔS≠) at the peak temperatures of the DSC curves were calculated. The structural stability could be illustrated from the point of thermodynamics and kinetics.

Graphical Abstract(1) Two novel zinc coordination architectures constructed from the primary ligand bib, Zn(II) transition metal ions and two carboxylate coligands. (2) The thermal decompositions properties of 1 and 2 were investigated by a simultaneous TG/DTG–DSC technique. The apparent activation energy E and the pre-exponential factor (A) of skeleton collapse for the complexes 1 and 2 are calculated by the integral Kissinger’s method and Ozawa–Doyle’s method. The structural stability could be illustrated from the point of thermodynamics and kinetics.Figure optionsDownload full-size imageDownload as PowerPoint slide