Synthesis, crystal structures and properties of two complexes constructed from in situ-generated new ligands

Two coordination complexes [Mn(ENA)2(H2O)0.5]n (1) and [Mn(EPDA)]n (2) have been synthesized and characterized by elemental analysis, IR, UV, TGA, DSC, PXRD and single crystal X-ray diffraction (ENA = 5-ethylnicotinate acid, EPDA = 5-ethylpyridine-2,3-dicarboxylic acid). In initial studies, Pmmi–ENA was selected to construct supramolecular compounds with metal ions (Pmmi = 5-isopropyl-2-methoxy-5-methylimidazolidin-4-one group). However, the Pmmi group was unexpectedly removed to result in the formation of a new ligand ENA, which coordinated with Mn(II) ions to form a 3D framework 1. In order to further investigate this interesting reaction, the same experiment was carried out with the homologous Imoi–ENA instead of Pmmi–ENA (Imoi–ENA and Pmmi–ENA are the homologous imazethapyr). Interestingly, the Imoi group was also removed, however, two different ligands ENA and EPDA were generated (Imoi = 2-(4-isopropyl-4-methyl-5-oxo-4,5-dihydro)-1H-imidazol-2-yl group). In addition, the photoluminescent properties of the two compounds were investigated in the solid state at room temperature.

Two new polymers have been constructed by performing the reactions of MnCl2 with Imoi–ENA at different reaction temperatures. The 3D compound 1, with μ3- and μ2-bridged ENA− ligands, could also be obtained by introducing Pmmi–ENA instead of Imoi–ENA. Complex 2 is a sandwich-like 2D coordination polymer with the inorganic (MnO4)n layer locating between the two organic layers.Figure optionsDownload as PowerPoint slideHighlights
► The compounds were based on the in situ-generated pyridyl-carboxylic ligands.
► Compound 1 can be obtained by performing the reactions using different reactants.
► ENA− and EPDA2− were derived from the decomposition of homologous imazethapyr.
► Different crystals can be obtained by controlling the reaction temperatures.