ERROR opening https://cactus.nci.nih.gov/chemical/structure/%5BO-2%5D.%5BO-2%5D.%5BO-%5D%5BO-%5D.%5BU%2B6%5D/file?format=sdf&get3d=True -- %5BO-2%5D.%5BO-2%5D.%5BO-%5D%5BO-%5D.%5BU%2B6%5D could not be loaded.