Spectroscopic and electrochemical properties of Cu-dicyandiamide complex

Abstract

Dicyandiamide (DICY) is a common ligand that exhibits low toxicity but can irritate the skin and eyes and cause methemoglobinemia on long-term exposure. Crystalline Cu-dicyandiamide (Cu-DICY) was obtained via facile synthesis and its molecular structure and theoretical Raman spectra were simulated by using density functional theory (DFT). The results suggested that the Cu²⁺ coordinates with two H₂O molecules and two different DICY molecules (an imino DICY and an amino DICY). The stability constants of Cu-DICY were calculated, and the electrochemical properties were studied. Two electro-chemical redox processes occur in Cu-DICY in an aqueous solution: a reversible reaction with a formal potential of 0.2 V vs. MSE and an irreversible reaction between –0.4 and –1.2 V vs. MSE. The standard rate constant k⁰ for the reversible reaction was estimated to be 7.6×10^–3 cm/s. In addition, based on the reversible reaction of Cu-DICY, square wave voltammetry was used to rapidly determine the concentration of Cu(II) and the detection limit was 66.7 μg/L, which satisfies the detection limit requirements for copper in tap water (2 mg/L) as provided by the World Health Organization.