Synthesis, structures, and thermodynamics/kinetics properties of three Zn(II) coordination polymers modified by 5-substituted isophthalic acid

摘要

Solvothermal reactions of flexible 1,6-bis(2-methyl-imidazol-yl)hexane (bimh), Zn(II) acetate and different 5-substituted isophthalic acids in ethanol/water (EtOH:H2O = 4:1) solvent system yielded three novel Zn(II) coordination polymers with different nuclearity: [Zn(bimh)(0.5)(5-mipa)]n (1), [Zn-2(bimh)(1.5)(5-tbipa)(2)]n (2) and [Zn-3(mu(3)-OH)(2)(bimh)(0.5)(5-nipa)(2)](n) (3) (5-H2mipa = 5-methylisophthalic acid, 5-H(2)tbipa = 5-tert-buty-isophthalic acid, 5-H(2)nipa = 5-nitroisophthalic acid). Compound 1 exhibits a 2-fold interpenetrating 3D pillared-layer network constructed from binuclear {Zn-2} units. Compound 2 features a 3D 2-fold interpenetrating architecture, which is a rare example of homometallic coordination polymers constructed by alternate mono/binuclear Zn(II) units. Compound 3 contains unusual [Zn-6(mu(3)-OH)(4)] units, which are extended by the 5-nipa2- and bimh ligands to construct a 3D framework. All compounds were prepared under exactly the same reaction conditions except the diverse substituent groups on 5-position of the isophthalic co-ligands. It has been found that the substituent groups profoundly influence the structural assemblies of the resulting compounds, in virtue of the related carboxylate groups displaying versatile coordination modes in binding metal ions. In addition, simultaneous TGDSC techniques were applied to assess the thermal decomposition behavior. Thermogravimetric measurements exhibit that compounds 13 possess excellent thermostability with high decomposition temperatures up to 314 degrees C, 370 degrees C and 306 degrees C, respectively. The kinetic parameters (apparent activation energy E and the pre-exponential factor A) of skeleton collapse for the compounds 13 were calculated by the Kissingers and OzawaDoyles methods. The thermodynamic parameters (Delta H#, Delta G#, and Delta S#) at the peak temperatures were also calculated. Furthermore, fluorescence properties of compounds 13 were investigated in solid state. (C