Chen, Shu-Yang, et al. “Synthesis, Crystal Structure and Luminescene of Zinc(II) Complex With 2,6-Pyridinedicarboxylic Acid Radical and 1,10-Phenanthroline”. Asian Journal of Chemistry, vol. 26, no. 21, Oct. 2014, pp. 7297-00, doi:10.14233/ajchem.2014.16615.