Alkaline reagent-induced structural diversity of four metal–organic frameworks based on a flexible bicarboxylate ligand

Abstract

Four new metal–organic frameworks, namely, [CdNa(bci)(H2O)3]n (1), [CdK(bci)(H2O)3]n (2), [Cd(Hbci)(H2O)]n (3) and {[(H2en)0.5Cd(bci)]·2H2O}n (4) (H3bci = bis(2-carboxyethyl)isocyanurate, en = ethylenediamine), have been prepared from H3bci and Cd(NO3)2 in aqueous solution using different alkaline reagents, namely, NaOH, KOH, triethylamine and ethylenediamine, respectively, which were characterized by single-crystal X-ray diffraction analyses, infrared spectroscopy, elemental analysis and powder X-ray diffraction. Compounds 1 and 2 are 3D heterometallic frameworks, featuring a 3-nodal 3,3,6-connected T5 type topology and a new 3-nodal 3,4,7-connected topology, respectively; complex 3 is a 3D monometallic framework with a uninodal 4-connected cag topology, while compound 4 is a 2D double-layer structure with a 2-nodal 3,6-connected kgd topology, which is extended to form a 3D supramolecular architecture by hydrogen bonds. Moreover, four new coordination modes of the H3bci ligand were observed in complexes 1–4. The results indicate that the alkaline reagents play a crucial role in the diversity of the structures and coordination modes of the H3bci ligand. The luminescence properties and thermal stabilities of these compounds were further investigated. Unexpectedly, complex 4 shows strong luminescence emission of guest ethylenediamine molecules.