Preparations, crystal polymorphs and DFT calculations of N1,N1,N4,N4-tetraphenylbuta-1,3-diyne-1,4-diamine

A novel ynamine compound, N-1,N-1,N-4,N-4-tetraphenylbuta-1,3-diyne-1,4-diamine (2), was prepared and characterized by single crystal X-ray diffraction, H-1 and C-13 NMR. The compound had two crystal polymorphs and they were solved successfully. There were two independent molecules in both polymorphs and the four kinds of molecules had a similar structure. The difference in crystal packing was found to originate in C-H center dot center dot center dot-pi interactions. The geometries obtained by DFT calculations showed a good agreement with the observed one, but a significant difference was recognized at the twist angles between the planes which were formed by the nitrogen atom and the connecting three carbon atoms. The dependence of the energy on the twist angle was also calculated by DFT method. The result indicated that the energy showed little change in the twist angle between 70 degrees and 90 degrees and that the molecular structure of 2 could change easily by packing force within the range. (C) 2013 Elsevier B.V. All rights reserved.