New Zn(ii) coordination polymers with 1,3-bis(4-pyridyl)-propane: syntheses, crystal structures and properties

Abstract

The ambient reactions of Zn(NO3)2·6H2O, 1,3-bis(4-pyridyl)-propane (bpp) and NaOH with benzoic acid, phenylacetic acid, phthalic acid, acetylenedicarboxylic acid afforded {Zn(bpp)(C6H5COO)2}·2H2O 1, Zn(bpp)(C6H5CH2COO)22, {Zn2(bpp)2[C6H4(COO)2]2}·2H2O 3 and Zn(bpp)(C4O4) 4. Except 2, which crystallizes in a centrosymmetric space group P21/n (no. 14), compounds 1, 3 and 4 crystallized in the acentric space groups Aba2 (no. 41), P21 (no. 4) and C2221 (no. 20), respectively. Compounds 1 and 2 feature 1D zigzag chains {[Zn(C6H5COO2](bpp)2/2} and {[Zn(C6H5CH2COO2](bpp)2/2}, respectively, generated from [Zn(C6H5COO)2] and [Zn(C6H5CH2COO)2] moieties bridged by bpp ligands. In 3, the phthalato bridged helical chains {Zn[C6H4(COO)2]2/2} are interlinked by TT- and TG-bpp ligands to form 3D MOF {Zn[C6H4(COO)2]2/2(TT-bpp)2/2(TG-bpp)2/2} with a (65·8) CdS topology. The acetylenedicarboxylato bridged helical chains {Zn[C2(COO)2]2/2} in 4 are interconnected by the bpp ligands to generate 3D MOF {Zn[C2(COO)2]2/2(TT-bpp)2/2} with a (66) diamond topology, and the formed crystal structure displays a four-fold interpenetration of the 3D MOF. Complexes 1, 3 and 4 exhibit significant ferroelectric behaviour (for 1 remnant polarization 2Pr = 3.97 × 10−4 μC cm−2, coercive field 2Ec =0.47 kV cm−1, saturation of the spontaneous polarization Ps = 2.63 × 10−3 μC cm−2; for 3 2Pr = 1.30 × 10−3 μC cm−2, 2Ec =1.02 kV cm−1, Ps = 5.42 × 10−3 μC cm−2; for 4 2Pr = 4.97 × 10−4 μC cm−2, 2Ec =0.46 kV cm−1, Ps = 2.08 × 10−3 μC cm−2). Additionally, 1 and 3 are verified to be SHG active. Furthermore, results about IR spectra, thermal analyses and fluorescence spectra were discussed.