Dong, Wen-Kui, et al. “Synthesis and Supramolecular Structure of 5,5’-Dihydroxy-2,2’-[1,1’-(propane-1,3-diyldioxydinitrilo)dimethylidyne]diphenol”. Asian Journal of Chemistry, vol. 25, no. 8, Mar. 2013, pp. 4398-00, doi:10.14233/ajchem.2013.13990.