A novel colorimetric sensor of dihydrogen-phosphate based on metal complex between 8-hydroxy quinoline-5-azo-4′-nitrobenzene and cobalt

A novel colorimetric sensor based on 8-hydroxy quinoline-5-azo-4′-nitrobenzene (1) was prepared and used for recognizing anions. 1 and its metal complex (1·Co) were found to show response to anions such as CH3CO2−, H2PO4−, HSO4−, F− and dramatic color changes were observed. The selectivity and sensitivity of 1 and 1·Co for sensing anions were different, which was in the order of CH3CO2− > F− > H2PO4− ≫ HSO4− for 1 and H2PO4− > HSO4− > CH3CO2− ∼ F− for 1·Co, respectively. In CH3CN, sensor 1·Co exhibited excellent specificity toward H2PO4−, and the color variety was dependent on the concentration of H2PO4− which was attributed to anion structure and stability of anionic complex (1-anion), metal complex (1-Co) and inorganic complex (Co-anion).