Two novel lead(ii)-tetrazolate frameworks based on cubane [Pb4(OH)4]4+ clusters trapping long lifetime luminescence emission

Abstract

Two novel Pb(II)-based metal–organic frameworks (MOFs) based on the rigid bitetrazolate ligand 1,4-benzeneditetrazol-5-yl (H₂BDT) have been synthesized under hydrothermal conditions and fully characterized. In these two compounds, [Pb₄(OH)₄(BDT)₂]·2H₂O (1) and [Pb₄(OH)₄(BDT)]·BDT·2H₂O (2), the H₂BDT ligands exhibit three different coordination modes which are firstly reported in M-BDT frameworks, constructing disparate architectures by bridging the same cubane-shaped [Pb₄(OH)₄]⁴⁺ building units. Compound 1 features a 3D supramolecular network with a rare 2-fold interpenetrating (10, 3)-d (or utp) topology which is accomplished by connecting [Pb₄(OH)₄]⁴⁺ clusters to μ₄-bridging BDT²⁻ ligands via weak bonds. Compound 2 exhibits a 2D square grid with (4, 4) topology and the adjacent 2D networks are further linked by Pb–O weak bonds to generate the 3D supramolecular structure. Moreover, the structures of these two compounds are highly influenced by the concentration of the starting reagents. Compounds 1 and 2 exhibit strong solid-state fluorescent emission with millisecond luminescence lifetimes at room temperature.