Four Alkali-Induced 3D Strontium(II) Coordination Polymers Constructed from Imidazole-4,5-dicarboxylate: Syntheses, Crystal Structures, and Properties

Four alkali-induced 3D coordination polymers, namely [Sr(HIDC)(H3IDC)(H2O)](n)center dot nH(2)O (1), [Sr(HIDC)](n) (2), [Sr-3(HIDC)(2)(H2IDC)(4)](n) (3), and [Sr-2(HIDC)(2)](n) (4), were constructed from strontium(II) and imidazole-4,5-dicarboxylic acid (H3IDC) and were characterized by elemental analysis, IR, TG, PL, powder and single-crystal X-ray diffraction. Complex 1 is an eca net with the Schlafli symbol of (3(9).4(12).5(7)) by considering the Sr-II cation as an 8-connected node. Complex 2 presents a rare 5-connected network with Schafli symbol of (4(5).6(5)) when the Sr-II cation and HIDC2- dianion are viewed as 5-connected nodes. Complex 3 is a complicated 3D network, which can be regarded as a H2IDC- monoanion sustained porous framework filled by another HIDC2- dianion and H2IDC- monoanion. Complex 4 exhibits a 3D porous framework with 1D trigonal hydrophobic channels. The ligand H3IDC in the four complexes exists as the H3IDC molecule, the H2IDC- monoanion, and the HIDC2- dianion. In addition, the mu(2) (kappa N-1:kappa O-1:kappa O-1) mode of the H3IDC molecule in complex 1, the mu(3) (kappa O-1:kappa O-1:kappa O-1:O-1) and mu(3) (kappa N-1:kappa O-1:kappa O-1:kappa O-1) modes of the H2IDC- monoanion in complex 3, as well as the mu 5 (kappa N-1:kappa O-2:kappa O-1:kappa O-2:kappa O-1) and mu 6 (kappa N-1:kappa O-2:kappa O-2:kappa O-2:kappa O-2) modes of the HIDC2- dianion in complexes 2 and 4 are reported for the first time. Diverse topological architectures of the four complexes depend mainly on the coordination spheres of the Sr-II cation, the coordination modes of the anions, the different alkali, and the ligand to alkali ratio. TG analysis indicates that complex 2 presents high thermal stability, while the TG curve and temperature-dependent PXRD spectra of complex 4 indicate that its framework is stable up to 350 degrees C. Moreover, the solid-state luminescent properties demonstrate that complexes 1 to 4 exhibit strong blue emission at room temperature.