A series of bis-pyridyl-bis-amide-modulated metal–organic frameworks: formation, transformation and selectivity for the efficient detection of multiple analytes

Abstract

The designing of luminescent metal–organic frameworks (LMOFs) as sensors for the detection of molecules and ions constitutes an active area of research. Four different three-dimensional (3D) unusual LMOFs, namely, {[Zn(3-pda)(TA)]·H₂O}_n (1), {[Zn(4-pda)(TA)]·2H₂O}_n (2), [Cd(3-pda)(TA)]_n (3), and {[Cd₂(4-pda)₂(TA)₂]·(4-fpia)·H₂O}_n (4) (3-pda = 1,4-bis(3-pyridylcarboxylamide)benzene, 4-pda = 1,4-bis(4-pyridylcarboxylamide)benzene, 4-fpia = N-(4-formylamino-phenyl)-isonicotinamide, and TA = terephthalic acid) were successfully synthesized by a hydrothermal method and characterized by single-crystal X-ray diffraction. Under solvothermal conditions, a structurally transformational 3D 3-fold interpenetrated porous MOF, [Cd₂(4-pda)₂(TA)₂(DMF)]_n (4a), was obtained, which could be further transformed to isostructural [Cu₂(4-pda)₂(TA)₂(DMF)]_n (4b) by single-crystal to single-crystal (SCSC) transformation. The effect of N-donor ligands, metal ions and solvents on the structure of MOFs is discussed in detail. A series of luminescence recognition tests proved that complexes 1–4 can be used as luminescent sensors for detecting certain metal cations, oxyanions, and toxic organic solvents in an aqueous environment. Furthermore, the luminescence quenching mechanism and structure–function relationship were studied systematically.