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.