N,N'-Bis(2-methoxybenzylidene) adducts of ethane-1,2-diamine, propane-1,3-diamine and butane-1,4-diamine.

We have isolated and crystallographically characterized the three homologous compounds N,N'-bis(2-methoxybenzylidene) ethane-1,2-diamine (MeSalen), C₁₈H₂₀N₂O₂, N,N'-bis-(2-methoxybenzylidene)propane-1,3-diamine (MeSalpr), C₁₉-H₂₂N₂O₂, and N,N'-bis(2-methoxybenzylidene)butane-1,4-diamine (MeSalbu), C₂₀H₂₄N₂O₂. In contrast with MeSalpr, the molecules of MeSalen and MeSalbu, which have an even number of methylene units, have crystallographic '1' symmetry. Comparing these methoxy-substituted species with their hydroxy equivalents shows that the aryl rings rotate upon removal of the O-H···N hydrogen bonds. The packing of MeSalen and MeSalpr is controlled by C-H···π interactions, whereas that of MeSalbu has only van der Waals contacts.