Hydrothermal synthesis of zinc(II)-phosphonate coordination polymers with different dimensionality (0D, 2D, 3D) and dimensionality change in the solid phase (0D→3D) induced by temperature

•Compounds have been obtained modifying the reaction time and the rate of reagents.•Dimensionality and crystalline structure is a function of the zinc environments.•New coordination modes for 2-carboxyethylphosphonic acid are reported.•3D-compound presents three different coordination environments for the zinc atoms.•Fluorescence properties are related to the structural dimensionality.

Three new zinc(II) coordination polymers, [Zn(HO3PCH2CH2COO)(C12H8N2)(H2O)] (1), [Zn3(O3PCH2CH2COO)2(C12H8N2)](H2O)3.40 (2) and [Zn5(HO3PCH2CH2COO)2(O3PCH2CH2COO)2(C12H8N2)4](H2O)0.32 (3), with different structural dimensionality (0D, 2D and 3D, respectively) have been prepared by hydrothermal synthesis, and their structures were determined by single-crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic system (P21/c) forming discrete dimeric units bonded through H-bonds, while compounds 2 and 3 crystallize in the triclinic (P−1) and the monoclinic (C2/c) systems, respectively. Compound 3, showing three different coordination numbers (4, 5 and 6) for the zinc atoms, has also been obtained by thermal treatment of 1 (probed by high-temperature XRPD experiments). The crystalline features of these compounds, related to the coordination environments for the zinc atoms in each structure, provoke the increase of the relative fluorescence for 2 and 3, compared to the free phenanthroline. Thermal analysis (TG and DSC) and XPS studies have been also carried out for all compounds.

Graphical abstractThree new coordination compounds of zinc with 2-carboxyethylphosphonic acid (H2PPA) and phenanthroline have been obtained by hydrothermal synthesis. The crystalline structure depends on the different coordination environments of the zinc atoms (see two comparative Zn6-moieties). The influence of the different coordination modes of H2PPA with the central atom in all structures have been studied, being found new coordination modes for this ligand. Several compounds show a significant increase in relative fluorescence with respect to the free phenanthroline.Figure optionsDownload full-size imageDownload as PowerPoint slide