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

Abstract

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.