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), C19H22N2O2, 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.pi interactions, whereas that of MeSalbu has only van der Waals contacts.