Towards correlating dimensionality and topology in luminescent MOFs based on terephthalato and bispyridyl-like ligands

Abstract

Herein, we report on the synthesis, structural analysis, physicochemical characterization and photoluminescence performance of two ternary compounds based on dicarboxylate and bispyridyl-like ligands and metal ions of group 12, namely [Zn₂(μ₄-bdc)(μ-pbptz)(DMF)₂(NO₃)₂]_n (1-Zn) and {[Cd(μ₃-bdc)(μ-pbptz)]·DMF}_n (2-Cd) (where bdc = benzene-1,4-dicarboxylate, pbptz = 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine, and DMF = N,N-dimethylformamide). 1-Zn, consisting of a 2D-layered framework, can be considered as the lower-dimensional analogue of the previously reported {[Zn₂(μ₄-bdc)₂(μ-pbptz)]·2DMF·3H₂O}_n 3D MOF (1′-Zn), which is shown to recrystallize into 1-Zn undergoing a kind of exfoliation. 2-Cd presents a 3D doubly interpenetrated framework whose porosity is reduced to approximately half of the available solvent-accessible voids contained in the non-interpenetrated homologue reported so far, {[Cd(μ₃-bdc)(μ-pbptz)]·3DMF}_n (2′-Cd). Structural factors leading to each of the alternative frameworks are detailed by analysing the building units with a perusal of the Cambridge Structural Database and providing a comparative description of the structures. The photoluminescence properties of herein reported compounds (1-Zn and 2-Cd) are also measured and the processes governing the spectra are described using time-dependent density-functional theory (TD-DFT), which allows establishing some structural correspondences by comparing these results with those of the 1′-Zn and 2′-Cd analogues.