6ADV:
reference: Hybridization and Mismatch Discrimination Abilities of 2',4'-Bridged Nucleic Acids Bearing 2-Thiothymine or 2-Selenothymine Nucleobase., Habuchi T, Yamaguchi T, Aoyama H, Horiba M, Ito KR, Obika S, J Org Chem. 2019 Feb 1;84(3):1430-1439. doi: 10.1021/acs.joc.8b02863. Epub 2019, Jan 24. PMID: 30632750

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).