ERROR opening https://cactus.nci.nih.gov/chemical/structure/C1%3DNC2%3DC%28N1%29C%28%3DNC%3DN2%29N/file?format=sdf&get3d=True  -- C1%3DNC2%3DC%28N1%29C%28%3DNC%3DN2%29N could not be loaded.