Kumar, Ashish, et al. “Synthesis, Spectral and Antibacterial Studies of 4-Aminoantipyrine Based Tetradentate Ligand and Its Cu(II), Ni(II) and Co(II) Metal Complexes”. Asian Journal of Chemistry, vol. 23, no. 10, Aug. 2011, pp. 4494-6, https://asianpubs.org/index.php/ajchem/article/view/10891.