Feng Ding, Cai, et al. “Synthesis and Crystal Structure of Tetra[pyridine]diperchlorato-K2 O-Cadmium(II)”. Asian Journal of Chemistry, vol. 18, no. 3, Mar. 2010, pp. 1685-9, https://asianpubs.org/index.php/ajchem/article/view/20856.