Syntheses, Structures, and Luminescent Properties of Zinc(II) and Cadmium(II) Coordination Complexes Based on Different (Pyridyl)imidazole Derivatives and 1,4-Benzenedicarboxylate

A series of mixed-ligand coordination complexes, namely, [Zn(L1)2(p-BDC)] (1), [Cd(L1)2(p-BDC)] (2), [Zn(L2)(p-BDC)] (3), [Cd(L2)(p-BDC)] (4), and [Zn2(L3)(p-BDC)1.5(OH)]·H2O (5) (L1 = 2-chloro-5-((2-(pyridin-2-yl)-1H-imidazol-1-yl)methyl)pyridine, L2 = 2-(1-(pyridin-3-ylmethyl)-1H-imidazol-2-yl)pyridine, L3 = 2-(1-(pyridin-4-ylmethyl)-1H-imidazol-2-yl)pyridine, and p-BDC = 1,4-benzenedicarboxylate), have been synthesized under hydrothermal conditions. Their structures have been determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. Compounds 1 and 2 are isostructural and show infinite chains which extend into two-dimensional (2D) supramolecular sheets by π···π interactions. For 3, L2 ligands link ZnII ions to form dimeric units [Zn2(L2)2] which are connected by p-BDC anions to form 63 layers which interpenetrate each other in a vertical manner to generate a rare 2D → three-dimensional (3D) polycatenated net. In 4, similar dimeric units [Cd2(L2)2] formed by L2 ligands and Cd cations which are linked by p-BDC ligands to give a unique 3D 3-fold interpenetrated (10,3)-b network structure. In 5, two kinds of p-BDC ligands coordinate to Zn cations to form a 2-fold interpenetrating network with α-Po topological structure, in which each L3 ligand coordinates to a Zn ion acting as a terminal ligand. By careful inspection of the structures of 1−5, we believe that the coordination geometries of metal centers and different substituent groups of N-donor ligands adopting various coordination modes are crucial factors for the formation of the different structures. The photoluminescent properties of L1−L3 and 1−5 have been studied in the solid state at room temperature.