Molecular Recognition of Biologically Relevant Anions with an Expanded Dinuclear Copper(II) Complex: An Efficient Sensor for Oxalate Anion in Aqueous Solution

Abstract

An expanded dinuclear copper(II) complex (1) derived from a biphenyl‐based hexaazamacrocyle (L) was synthesized and characterized by single crystal X‐ray analysis, exhibiting a boat‐shaped cavity with an elongated CuII⋅⋅⋅CuII distance of 11.01 Å. The dinuclear copper(II) complex was investigated for a verity of biologically relevant anions including carboxylates (oxalate, citrate, tartrate, glutamate, adipate, acetate and benzoate), oxoanions (phosphate, sulphate, perchlorate and nitrate), and halides (fluoride, chloride, bromide and iodide) by competitive fluorescence titrations via indicator displacement assay (IDA) using an external dye (Eosin Y) in water‐methanol solution at neutral pH. The receptor was shown to exhibit strong affinity for oxalate, providing the binding trend: oxalate (log K=6.07)>citrate (log K=5.74)>phosphate (log K=5.02)>tartrate (log K=4.78)>glutamate (log K=4.42)>adipate (log K=4.31)>acetate (log K=4.14)>benzoate (log K=4.01). No interaction was observed for other anions including sulphate, perchlorate, nitrate, fluoride, chloride, bromide and iodide under the identical conditions.