A theoretical investigation of the competition between hydrogen bonding and lone pair•••π interaction in complexes of TNT with NH3

A theoretical study of the interactions between 2,4,6-trinitrotoluene (TNT) and ammonia (NH3) has been carried out by means of MP2, DFF, and CCSD(T) methods. Eight stable structures of TNT center dot center dot center dot NH3 complexes were identified at the MP2/6-311++G(d,p) level. Various interactions such as lone pair center dot center dot center dot pi interaction (lp center dot center dot center dot pi interaction), conventional N-H center dot center dot center dot O, C-H center dot center dot center dot N, N-H center dot center dot center dot pi hydrogen bonds, and novel noncovalent C center dot center dot center dot N carbon bonding, have been observed in the titled complexes. The competition between hydrogen bonding and lp center dot center dot center dot pi interaction in the complexes was studied and discussed. The attractive Ip center dot center dot center dot pi interactions are observed when the lone pair of NH3 points toward TNT pi ring. At the CCSD(T)/6-311++G(d, p)//MP2/6-311++G(d,p) level, the corresponding BSSE corrected interaction energy (Delta E) is -3.7 kcal mol(-1). The calculated results also show that the lp center dot center dot center dot pi interaction competes successfully with the N-H center dot center dot center dot pi and N-H center dot center dot center dot O hydrogen bonds. The competition between hydrogen bonding and lp center dot center dot center dot pi interaction in TNT center dot center dot center dot NH3 complexes plays important role to affect the structures of complexes. However, the conventional C-H center dot center dot center dot N hydrogen bond is stronger than the lp center dot center dot center dot pi interaction. The complex I merely with C-H center dot center dot center dot N hydrogen bond is the most stable structure among eight complexes. The theoretical studies on UV and IR spectra of the TNT center dot center dot center dot NH3 complexes show that the formations of hydrogen bonding and lp center dot center dot center dot pi interaction have small effect on the UV spectra but new IR absorption peaks in range of 100-300 cm(-1) correlated to interactions between TNT and NH3 have been predicted, which may be helpful for the detection of TNT. (C) 2015 Elsevier &V. All rights reserved.