Conformational analysis and intramolecular/intermolecular interactions of N,N′-dibenzylideneethylenediamine derivatives

The molecular structures, conformational stability and molecular energy profile of three derivatives of RC6H4CHNCH2CH2NCHC6H4R including N,N′-dibenzylideneethylenediamine (1, R = H), N,N′-bis(4-trifluoromethoxybenzylidene)ethylenediamine (2, R = OCF3), and N,N′-bis(4-dimethylaminobenzylidene)ethylenediamine (3, R = N(CH3)2) were obtained at B3LYP/6-31++G** and HF/6-31++G** levels of theory and compared with X-ray single crystal structures. The conformation of 1 and 2 is anti, while that of 3 is gauche in solid state (X-ray geometry). Based on calculations, there are seven energy minima in potential energy curves. A gauche conformer of 1, 2 and 3 has the lowest energy minimum (in the calculations modeling gas phase conditions) among all the other conformers. This is in contrast to X-ray findings (solid phase) for 1 and 2 but complements the X-ray finding for 3. These results were analyzed by natural bond orbital (NBO) and molecular orbital (MO) to determine the role of intra- and/or intermolecular interactions in the crystal structures.