Synthesis, structure and photoluminescence properties of heterometallic-based coordination polymers of trimesic acid

Reacting trimesic acid (H₃TMA, C₉H₆O₆) with CaCl₂ and MCl₂ at 110 °C under hydrothermal conditions gave the isostructural heterobimetallic coordination polymers (CPs) catena-poly[[tetraaquazinc(II)]-μ-5-carboxybenzene-1,3-dicarboxylato-[tetraaquacalcium(II)]-μ-5-carboxybenzene-1,3-dicarboxylato], [CaZn(HTMA)₂(H₂O)₈]_n, 1, and catena-poly[[tetraaquacobalt(II)]-μ-5-carboxybenzene-1,3-dicarboxylato-[tetraaquacalcium(II)]-μ-5-carboxybenzene-1,3-dicarboxylato], [CaCo(HTMA)₂(H₂O)₈]_n, 2. Compounds 1 and 2 crystallize in the monoclinic space group C2/c. The solid-state structures consist of eight-coordinate Ca^II ions and six-coordinate M^II ions. These ions are connected by a doubly deprotonated HTMA^2- ligand to create a one-dimensional (1D) zigzag chain. Poly[[decaaquabis(μ₃-benzene-1,3,5-tricarboxylato)calcium(II)dizinc(II)] dihydrate], {[CaZn₂(TMA)₂(H₂O)₁₀]·2H₂O}_n, 3, was found incidentally as a minor by-product during the synthesis of 1 at a temperature of 140 °C. It forms crystals in the orthorhombic space group Ccce. The structure of 3 consists of a two-dimensional (2D) layer composed of [Zn(TMA)] chains that are interconnected by Ca^II ions. The presence of aromatic carboxylic acid ligands and water molecules, which can form numerous hydrogen bonds and π-π interactions, increases the stability of the three-dimensional (3D) supramolecular architecture of these CPs. Compounds 1 and 2 exhibit thermal stability up to 420 °C, as indicated by the thermogravimetric analysis (TGA) curves. The powder X-ray diffraction (PXRD) data reveal the formation of unidentified phases in methanol and dimethyl sulfoxide, while 1 exhibits chemical stability in a wide range of solvents. The luminescence properties of 1 dispersed in various low molecular weight organic solvents was also examined. The results demonstrate excellent selectivity, sensitivity and recyclability for detecting acetone molecules in aqueous media. Additionally, a possible sensing mechanism is also outlined.