Solution structure, crystal structure, Hirshfeld surface analysis of copper(II) diamide species as an optical chemical sensor

Abstract

Optical chemical sensors are promising tools for the detection of metal ions in various samples. Copper(II) has received significant attention among metal ions due to its toxic nature and widespread applications in various industrial processes. In recent years, several optical chemical sensors have been developed to detect copper(II) with high sensitivity and selectivity. This paper describes the spectrophotometric determination of trace amounts of copper(II) using N1-(2-aminoethyl)-N2-((pyridin-2-yl)methyl)oxalamide (H2(555)NH2) as an optical chemical sensor. The protonation and formation constants of the Cu(II)/(H2(555)NH2) system were determined at 25 °C and the ionic strength of 0.15 mol dm−3 using glass electrode potentiometry. The structures of the different species, present in solution at different pH values, were determined using UV–vis, 1H NMR, and EPR spectroscopic techniques. At pH 5, the [Cu(H2(555)NH2)]2+ species was formed with the Cu(II) coordinated to the pyridole nitrogen and the terminal amine. Above pH 8, [Cu(H2(555)NH2)H-2] is the most predominant species in solution. Here the Cu(II) coordinates to all four nitrogen atoms. In the solid state, a dinuclear complex, [Cu(H(55)NH3)Cl]2[Cu(H2O)2(NO3)2Cl2]H2O, was formed. Single crystal X-ray structure showed the Cu(II) to be coordinated to the pyridine and the amide N-atoms in addition to an O-atom from one of the two carbonyl groups. The coordination environment was completed by two bridged chloride ions to give a slightly distorted trigonal bipyramidal coordination geometry around the copper centre. The amine was not coordinated. The proposed sensor was successfully applied to determine copper(II) in real samples, with recoveries ranging from 10−5 to 10−3 mol/dm−3. Using H2(555)NH2 as an optical chemical sensor emerged as a powerful tool for detecting copper(II) ions in different aqueous samples.