Novel alkali and alkaline earth metal coordination polymers based on 1,4-naphthalenedicarboxylic acid: synthesis, structural characterization and properties

Abstract

Six new alkali and alkaline earth metal coordination polymers based on rigid 1,4-naphthalenedicarboxylic acid (H₂NDA), [Li(HNDA)(H₂O)₂] (1), [Na₂(NDA)(DMF)] (2), [Mg₂(NDA)₂(H₂O)₃]·0.25H₂O (3), [Ca(NDA)(DMF)] (4), [Sr(NDA)(DMF)] (5), and [Ba(NDA)(DMF)] (6) have been synthesized under solvothermal conditions in order to evaluate the coordination behavior of H₂NDA towards Li⁺, Na⁺, Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ ions and the structural features of the resulted polymeric complexes. Their structures were determined by single-crystal X-ray diffraction studies. The coordination number of the metal ions varies from 4 (for Li), 5 (for Na), 6 (for Na and Mg) to 7 (for Ca, Sr, and Ba), while the number of metal ions bound to the ligand ranges from 2 (Li), 4 (Mg), 5 (Ca, Sr, and Ba) to 8 (Na). Compound 1 has a one-dimensional polymeric structure which is further connected by hydrogen bonds to form a supramolecular assembly. Compound 2 is a three-dimensional metal–organic framework (MOF) possessing hexagonal channels which are built up by helical 1D infinite inorganic chains connected with NDA ligands. Interestingly, the porous MOF, 2, exhibited high gas sorption properties for CO₂ over N₂. Compound 3 has a three-dimensional structure having 1D inorganic chains connected with NDA ligands in two directions to form a cage-like structure. Compounds 4, 5 and 6 are isostructural, having three-dimensional structures in which 1D inorganic chains are connected by NDA to form a 2-nodal 5,5-connected net. In addition, the solid state photoluminescence properties of all the compounds have also been studied.