A new three-dimensional barium(II) coordination polymer constructed from <i>N</i>,<i>N</i>′-bis(glycinyl)pyromellitic diimide: microwave-assisted synthesis, structure, Hirshfeld surface analysis and properties

A new three-dimensional (3D) coordination polymer, namely, poly[diaqua[μ₅-2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetato]barium(II)], [Ba(C₁₄H₆N₂O₈)(H₂O)₂]_n, (I), has been synthesized by the microwave-irradiated reaction of Ba(NO₃)₂ with N,N'-bis(glycinyl)pyromellitic diimide {BGPD, namely, 2,2'-(1,3,5,7-tetraoxo-1,2,3,5,6,7-hexahydropyrrolo[3,4-f]isoindole-2,6-diyl)diacetatic acid, H₂L}. The title compound was structurally characterized by single-crystal X-ray diffraction analysis and powder X-ray diffraction analysis, as well as IR spectroscopy. In the crystal structure of (I), the Ba^II ion is nine-coordinated by six carboxylate O atoms from five symmetry-related L^2- dianions and one imide O atom, as well as two water O atoms. The coordination geometry of the central Ba^II ion can be described as a spherical capped square antiprism. One carboxylate group of the ligand serves as a μ₃-bridge linking the Ba^II cations into a one-dimensional polynuclear secondary building unit (SBU). Another carboxylate group of the ligand acts as a μ₂-bridge connecting the 1D SBUs, thereby forming a two-dimensional (2D) SBU. The resulting 2D SBUs are extended into a 3D framework via the pyromellitic diimide moiety of the ligand as a spacer. The 3D Ba framework can be simplified as a 5-connected hexagonal boron nitride net (bnn) topology. The intermolecular interactions in the 3D framework were further investigated by Hirshfeld surface analysis and the results show that the prominent interactions are H...O (45.1%), Ba...O (11.1%) and C...H (11.1%), as well as H...H (11.1%) contacts. The thermal stability, photoluminescence properties and UV-Vis absorption spectra of (I) were also investigated. The coordination polymer exhibits a fluorescence emission with a quantum yield of 0.071 and high thermal stability.