Two fluorescent coordination polymers constructed from mixed rigid and flexible carboxylate ligands: Formation of cross-linking helical and zigzag chains

Two 3D coordination polymers with different structure motifs, [Zn2(PCPA)2(IN)2]n (1) and [Co(PCPA)(IN)]n (2) (PCPA=p-chlorophenoxyacetate, IN=isonicotinate), first constructed from mixed rigid and flexible carboxylate ligands, have been obtained under hydrothermal condition and characterized by elemental analyses, IR spectra, thermogravimetric analysis, fluorescent spectra and single crystal X-ray diffraction analysis. The most intriguing structural feature is that each complex exhibits both infinite helical Zn(μ2-carboxylate) or Co(μ3-carboxylates) chain units with 21 helices and zigzag M2(IN)2 (M=zinc and cobalt) chain units by reason of two different carboxylate ligands coordinating to metal centers. Additionally, compounds 1 and 2 show similar blue fluorescence in the solid state at room temperature.