ERROR opening https://cactus.nci.nih.gov/chemical/structure/%5BN-%5D%3D%5BN%2B%5D%3D%5BN-%5D.%5BK%2B%5D/file?format=sdf&get3d=True  -- %5BN-%5D%3D%5BN%2B%5D%3D%5BN-%5D.%5BK%2B%5D could not be loaded.