Four Novel Three-Dimensional Pillared-Layer Metal-Organic Frameworks in the Zn/Triazolate/Carboxylate System: Hydrothermal Synthesis, Crystal Structure, and Luminescence Properties

Abstract

Four novel zinc(II) metal-organic frameworks, {[Zn7(trz)6(1,3-bdc)4(H2O)2]·2H2O}n (1), {[Zn7(trz)6(hip)4(H2O)2]·8H2O}n (2), [Zn4(trz)4(Hnip)2(nip)]n (3), and [Zn5(trz)2(Hbtc)4(H2O)4]n (4) (Htrz = 1,2,4-triazole, 1,3-H2bdc = 1,3-benzenedicarboxylic acid, H2hip = 5-hydroxyisophthalic acid, H2nip = 5-nitroisophthalic acid, and H3btc = 1,3,5-benzenetricarboxylic acid), have been hydrothermally synthesized by reaction of Zn salt and Htrz with four different aromatic acids, respectively. Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by X-ray powder diffraction, elemental analyses, IR spectra, and TG analyses. The structures of compounds 1 and 2 are isostructural and feature the 3D structure containing multidimensional intersecting ring channels formed by the interconnection of 2D layers {[Zn7(trz)6]8+}n with 1,3-bdc (1) or hip (2). Compound 3 consists of {[Zn4(trz)4]4+}n layers with (4, 82) topology arranged in the −ABAB− stacking sequence, which are connected by nip pillars to generate a novel 3D open framework. Compound 4 is also in a 3D structure containing 2D layer motifs, which are further linked by btc ligands to complete the structure. There are two different building units [Zn2(trz)2]2+ and [ZnO6] within the 2D layers of 4. All of the compounds 1−4 exhibit the 3D pillared-layer structures. In the 2D layer motifs of these four compounds, trz ligands connect Zn ions in different coordination modes, which reflect the tendency of the trz ligand to bridge multiple metal sites, and the aromatic carboxylate ligands in compounds 1−4 serve as the pillar between the 2D layers, creating the 3D open frameworks. Moreover, these four compounds exhibit emission properties at room temperature in the solid state.