Three-pillared layer metal–organic frameworks assembled by imidazole-4,5-dicarboxylate and rigid bisimidazole ligands: synthesis, crystal structure, and sensing nitroaromatics

Abstract

Three-pillared layer metal–organic frameworks based on 1H-imidazole-4,5-dicarboxylate and linear bis(imidazole) ligands generally formulated as {[Co3(idc)2(bib)3]·8H2O}n (1), {[Cd(Hidc)(bib)0.5]}n (2) and {[Cd(Hidc)(bibp)]}n (3), where H3idc = 1H-imidazole-4,5-dicarboxylate, bib = 1,4-bis(1-imidazolyl)benzene and bibp = 4,4′-bis(1-imidazolyl)biphenyl, have been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Compound 1 features a 3-D-pillared layer structure with 1-D channels, generated by honeycomb-like 2-D layer linked by bib ligands. Compound 2 consists of 2-D lumpy layers of [Cd4(Hidc)4], which are further connected by bridging ligands of bib to generate a pillared layer 3-D framework with 1-D channels. In 3, the 2-D corrugated honeycomb networks, structurally analogous to CFx, are pillared by bibp ligands to form a 3-D architecture with 1-D channels. Through selecting different metal ions and the length of pillared ligands, the pore sizes are adjusted in the three complexes. The potential of 2 and 3 for nitro explosive sensing is investigated through luminescence quenching experiments, which show that 3 can be applied as a fluorescent sensor for nitro compounds.