Synthesis, Crystal Structure and Theoretical Calculations of Two Zn (II) Coordination Polymers Based on 2,5-Dihydroxyterephthalic Acid

Two new coordination polymers, namely [Zn2(phen)2(DHTA)]·2H2O (1) and [Zn2(PHDI)2(DHTA)]·2H2O (2) (phen = 1,10-Phenanthroline, PHDI = 1,10-Phenanthroline-5,6- dione, DHTA = 2,5-dihydroxyterephthalic acid) have been synthesized under hydrothermal conditions. The structures have been determined by single crystal X-ray diffraction, thermal gravimetric analysis, infrared spectrum and luminescent properties. The X-ray diffraction analysis revealed the coordination modes of Zn(II) centers from complexes (1) and (2) are different. In (1), there are unusual five coordinated and six coordinated Zn(II) ions. In (2), the center is four coordinated Zn (II). Through these coordination modes of Zn centers and the π–π stacking interactions of organic ligands, the two complexes are all connected to three-dimensional supramolecular networks. The solid-state photoluminescence properties of (1) and (2) have been investigated. The emission peaks are located at 538 and 603 nm, the emissions may be attributed to the metal-to-ligand charge-transfer. The quantum-chemical calculations have been performed on ‘molecular fragments’ extracted from the crystal structure using the B3LYP method in Gaussian 09.