Two new cadmium(II) coordination polymers based on imidazole-containing ligands: synthesis, structural characterization and fluorescence properties

The judicious selection of suitable ligands is vitally important in the construction of novel metal-organic frameworks (MOFs) with fascinating structures and interesting properties. Recently, imidazole-containing multidentate ligands have received much attention. Two new Cd-II coordination frameworks, namely, poly[tris{mu-1,4-bis [(1H-imidazol-1-yl)methyl]benzene-kappa N-2(3):N-3(')}tetrakis(nitrato-kappa O-2,O')dicadmium], [Cd-2(NO3)(4)(C14H4N4)(3)](n), (I), and poly[[bis{mu(3)-1,3,5-tris[(1H-imidazol-1-yl)methylibenzene-kappa N-3(3):N-3':N-3('')}cadmium] hexafluorosilicate], {[Cd(C18H18N6)(2)](SiF6)}(n), (II), have been synthesized and characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. In polymer (I), the 1,4-bis[(1H-imidazol-1-yl)methylibenzene ligand bridges Cd2+ ions with a distorted seven-coordinated pentagonal bipyramidal geometry, forming a one-dimensional ladder chain, and the nitrate anions coordinate to the Cd2+ ions in a terminal bidentate fashion. In the crystal, adjacent chains are further connected by C-H center dot center dot center dot O hydrogen bonds to generate a two-dimensional (2D) supramolecular structure. Polymer (II) exhibits a 2D layered structure in which 1,3,5-tris[(1H-imidazol-1-yl)methyl] benzene ligands join Cd2+ centres having a six-coordinated octahedral structure. The layers are connected by hexafluorosilicate anions via C-H center dot center dot center dot F hydrogen-bond interactions, giving rise to a three-dimensional supramolecular network structure in the solid state. In addition, powder X-ray diffraction (PXRD) patterns were recorded, thermogravimetric analyses (TGA) carried out and fluorescence properties investigated.