Stability study of the complex ion [Cu(opba-dCl)]2- in function of pH

The coordination compounds present a wide range of applications, among them we can highlight biological activity, catalysts, magnetic devices and sensors. Depending on the application the compound should have a stability in function of pH variation. For this purpose, the aim of this work is to evaluate the stability of Na2[Cu(opba-dCl)] as a function of pH by UV-vis absorption spectroscopy. An automatic titrator for pH control and an UV-vis spectrometer were used. The Uv-vis spectra were measured in the range of 400 to 1100 nm in a quartz cuvette at room temperature. It is possible to observe that when the pH is below 4.38, an abrupt increase occurs at the bottom line of the spectrum, caused by the presence of precipitated particles (Figure 1). Also in this same pH the solution shows a greenish coloration, which indicates the decomposition of the complex ion and the consequent formation of an insoluble coordination polymer. By analyzing the graph it was possible to define that the optimum pH range of work for this substance is 4.69 to 10.99. It suggests that in this range the complex does not decompose.