Construction of four 3d–4f heterometallic pillar-layered frameworks containing left- and right-handed helical chains and a I− chemosensor

Abstract

Four new heterometallic coordination complexes, namely, {[Zn₄Ln₂(imdc)₄(SO₄)(H₂O)₈]·4H₂O}_n [Ln = Nd (1), Sm (2), Eu (3), Gd (4); H₃imdc = imidazole-4,5-dicarboxylic acid], were hydrothermally synthesized by the reactions of Ln₂O₃ with imidazole-4,5-dicarboxylic acid and ZnSO₄·7H₂O and characterized by single-crystal X-ray diffraction, infrared spectroscopy (IR), elemental analysis (EA), thermogravimetric analysis (TGA) and powder X-ray diffraction (PXRD). The single-crystal X-ray diffraction analyses reveal that these polymers are isostructural and possess an interesting 3D pillar-layered architecture with 4²⁴·6⁴ topology, in which 2D layers constructed by alternately arranged 1D right-/left-handed helical chains of [Zn₂(μ₅-imdc)]_n bridged via dimeric Eu₂ units are pillared by μ₂-SO₄²⁻ and μ₃-imdc³⁻ anions. The liquid fluorescence of compounds 1–3 at room temperature shows that these complexes are very good chemosensors for I⁻ ion, and the response of the sensor is based on fluorescence quenching of Zn–Ln MOFs by iodine ions.