Sangeetha, J.E., et al. “Synthesis and Characterization of Transition Metal Complexes of 12- and 14-Membered Tetraaza Macrocycles”. Asian Journal of Chemistry, vol. 20, no. 6, Mar. 2010, pp. 4749-54, https://asianpubs.org/index.php/ajchem/article/view/19090.