Synthesis, Crystal Structure, and Luminescent Properties of New Zinc(II) and Cadmium(II) Metal-Organic Frameworks Based on Flexible Bis(imidazol-1-yl)alkane Ligands

Abstract

New metal-organic frameworks (MOFs) based on zinc and cadmium ions, terephthalic acid, and flexible ligands 1,5-bis(imidazol-1-yl)pentane or 1,6-bis(imidazol-1-yl)hexane were prepared and characterized by X-ray diffraction, thermorgavimetric analysis and IR spectroscopy. The imidazolyl ligands were prepared by a new robust procedure involving the reaction between imidazole and 1,5-dibromopentane or 1,6-dibromohexane in a superbasic medium (KOH in DMSO). MOFs based on 1,5-bis(imidazol-1-yl)pentane had diamond topology (dia) and are triply interpenetrated. Ligands with longer spacer 1,6-bis(imidazol-1-yl)hexane, terephthalate ions and zinc(II) ions formed five-fold interpenetrated metal-organic framework also with dia topology, while cadmium(II) ions with the same ligands formed eight-connected uninodal net with a very rare self-penetrated topological type ilc and a point symbol 424.5.63. The influence of the chemical composition of MOFs on their photoluminescent properties is investigated and discussed in detail.

Keywords

• imidazole
• bis(imidazol-1-yl)alkanes
• zinc
• cadmium
• metal-organic frameworks
• luminescence
• flexible ligands