Hydro/solvo-thermal syntheses and characterization of a series of CuII and CuI coordination polymers with an asymmetric semi-rigid Bi-functional ligand: Temperature induced polymorphism and photo-luminescent sensing

Abstract

In this work, a flexible asymmetric semi-rigid bi-functional ligand 5-(4-((1H-1,2,4- triazol-1-yl)methyl)phenyl)-1H-tetrazole (HL) has been employed. A series of unique CuII and CuI coordination compounds, namely [Cu(μ2-L)2(H2O)2]n (1), [Cu(μ2-L)2(H2O)2]n (2), [Cu(μ4-L)]n (3) and [Cu2.5(μ4-L)(CN)1.5]n (4), have been prepared under hydro(solvo)-thermal conditions. 1 and 2 present scarcely reported temperature induced polymorphic 1D (1) and 2D (2) copper(II)-L coordination frameworks. When HL and CuBr2 are employed to react in the mixed H2O/CH3CN (1:1) solvent system, the 3D CuI-HL coordination polymer 3 can be isolated. The CuI centers in 3 should be the reduction of CuII ions by CH3CN solvent. When CuBr is used to replace CuBr2 under similar synthetic conditions of 3, 4 can be isolated. 4 is a unique 3D CuI cluster-based coordination framework assembled from L− and CN−. PXRD patters of all the bulky samples 1–4 also have been determined, which agree well with theoretical PXRD patterns, confirming pure phases. Photo-luminescent measurements also show that complexes 3–4 can behave highly sensitive photo-luminescent sensing of small solvent molecules DMF and NMP. Additionally, 4 also exhibits highly selective and sensitive photo-luminescent discriminating of dichromate anions in aqueous solutions with excellent quenching efficiency (Ksv = 2.38 × 104 L mol-1). The experiment result also demonstrates the broad prospects in the preparation of these novel coordination frameworks using these flexible bi-functional asymmetric semi-rigid ligands as basic building blocks.