Crystal structures and thermodynamics/kinetics of Zn(II) coordination polymers with helical chains

Abstract Solvothermal reactions of Zn(II) acetates and four V-shaped carboxylates ligands in the presence of 1,4-Bis(2-methyl-imidazol-1-yl)butane afforded four interesting Zn(II) coordination polymers with helical chains, namely, {[Zn(bib)(atibdc)]·2H 2 O} n (1), {[Zn(bib)(atbip)]·H 2 O} n (2), [Zn(bib)(2,2′-tda)]} n (3) and {[Zn(bib)(5-tbipa)]·EtOH} n (4), (H 2 atibdc=5-amino-2,4,6-triiodoisophthalic acid, H 2 atbip=5-amino-2,4,6-tribromoisophthalic acid, 2,2′-H 2 tad=2,2′-thiodiacetic acid, 5-H 2 tbipa=5-tert-butyl-isophthalic acid). 1 reveals a 3D chiral framework with three kinds of helical chains along a , b and c axis. 2 shows a 2D step-type chiral framework with right-handed helical chains. 3 displays a wavelike 2D layer network possessing alternate left- and right-handed helical chains. 4 presents a four-connected 3D framework with zigzag and meso -helical chains. The different spacers and substituent group of carboxylic acid ligands may lead to the diverse network structures of 1 – 4 . The fluorescent properties of complexes 1 − 4 were studied. In addition, the thermal decompositions properties of 1 – 4 were investigated by simultaneous TG/DTG–DSC technique. The apparent activation energy E and the pre-exponential factor ( A ) of skeleton collapse for the complexes 1 – 4 are calculated by the integral Kissinger's method and Ozawa–Doyle's method. The activation energy E ( E 1 =209.658 kJ·mol −1 , E 2 =250.037 kJ mol −1 , E 3 =225.300 kJ mol −1 , E 4 =186.529 kJ·mol −1 ) demonstrates that the reaction rate of the melting decomposition is slow. The thermodynamic parameters (Δ H ‡ , Δ G ‡ and Δ S ‡ ) at the peak temperatures of the DTG curves were also calculated. Δ G ‡ >0 indicates that the skeleton collapse is not spontaneous. Δ H d >0 suggests that the skeleton collapse is endothermic, corresponding to the intense endothermic peak of the DSC curve. The structural stability could be illustrated from the point of thermodynamics and kinetics.