Dimensionality of luminescent coordination polymers of magnesium ions and 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylic acid modulated by structural inducing agents

Abstract

Solvothermal reactions of aromatic 1,1′-ethynebenzene-3,3′,5,5′-tetracarboxylic acid (H₄EBTC) and Mg²⁺ salts in the presence of different supporting ligands afforded the coordination polymers [Mg(H₂EBTC)(DMF)₂(H₂O)₂] (1), [Mg₃(HEBTC)₂(H₂O)₄]·solvent (2) and [Mg₂(EBTC)(H₂O)₅]·solvent (3). The crystal structures of 1–3 were determined by the single crystal X-ray diffraction technique, where CP 1 showed a one-dimensional zigzag MgO₆ coordination octahedral chain structure; 2 exhibited a two-dimensional MgO₆ coordination octahedral framework with trinuclear [Mg₃(COO)₆] SBUs, and 3 featured a three-dimensional MgO₆ coordination octahedral framework with binuclear [Mg₂O(COO)₂] SBUs. The various structures in CPs 1–3 of Mg²⁺ ions with the H₄EBTC ligand were ascribed to the conformational flexibility and the coordination mode diversity of the H₄EBTC ligand. Interestingly, the zwitterionic supporting ligand 2-aminoterephthalic acid or 4-aminobenzenesulphonic acid played a vital role in the initial formation process of nuclear crystals but only as a structural induction agent, which modulated the dimensionality of these Mg²⁺-based CPs. Additionally, the three CPs emitted bright blue luminescence at ambient conditions, and the emission lifetimes and absolute quantum yields were also investigated.