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.
Highlights
Ongoing research aimed at the design of new metal-organic frameworks (MOFs) is stimulated by their high capacity for gas storage and separation [1,2,3,4,5,6] photo-physical properties [7,8,9,10], sensor capabilities [11], excellent catalytic activity [12,13], medical imaging and drug delivery applications [14,15]
Functional properties of MOFs can be fine-tuned by careful choice of organic linkers, both rigid and flexible ligands are suitable for this aim [16]
The use of flexible ligands often hinders the formation of ordered 3D MOF structure, but on the other hand, conformationally mobile molecules can meet the geometrical demands of different metal coordination spheres and form structures otherwise inaccessible with rigid ligands [17]
Summary
Ongoing research aimed at the design of new metal-organic frameworks (MOFs) is stimulated by their high capacity for gas storage and separation [1,2,3,4,5,6] photo-physical properties [7,8,9,10], sensor capabilities [11], excellent catalytic activity [12,13], medical imaging and drug delivery applications [14,15]. Functional properties of MOFs can be fine-tuned by careful choice of organic linkers, both rigid and flexible ligands are suitable for this aim [16]. The use of flexible ligands often hinders the formation of ordered 3D MOF structure, but on the other hand, conformationally mobile molecules can meet the geometrical demands of different metal coordination spheres and form structures otherwise inaccessible with rigid ligands [17]. Poly(azole)-based ligands have been widely used for the construction of MOFs, but most of them act as anionic azolate linkers [18], while neutral bidentate ligands are less explored. Several papers reporting the use of bis(imidazol-1-yl) bis(1,2,4-triazol-1-yl) coordination polymers [19,20]
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