Cooperative Effects and Strengths of Hydrogen Bonds in Open-Chaincis-Triaziridine Clusters (n= 2−8):  A DFT Investigation

Abstract

We employ DFT/B3LYP method to investigate linear open-chain clusters (n = 2-8) of the cis-triaziridine molecule that is a candidate molecule for high energy density materials (HEDM). Our calculations indicate that the pervasive phenomena of cooperative effects are observed in the clusters of n = 3-8, which are reflected in changes in lengths of N...H hydrogen bonds, stretching frequencies, and intensities of N-H bonds, dipole moments, and charge transfers as cluster size increases. The n(N) --> sigma*(N-H) interactions, i.e., the charge transfers from lone pairs (n(N)) of the N atoms into antibonds (sigma*) of the N-H bonds acting as H-donors, can be used to explain the observed cooperative phenomena. The approaches based upon natural bond orbital (NBO) method and theory of atoms in molecule (AIM) to evaluating N...H strengths are found to be equivalent. In the process of N...H bonding, cooperative nature of n(N) --> sigma*(N-H) interactions promotes formation of stronger N...H bonds as reflected in increases in the capacities of cis-triaziridine clusters to concentrate electrons at the bond critical points of N...H bonds. The calculated nonadditive energies also show that the cooperative effects due to n(N) --> sigma*(N-H) interactions indeed provide additional stabilities for the clusters.

Density Functional Theory Study of the Properties of N−H···N, Noncooperativities, and Intermolecular Interactions in Linear trans-Diazene Clusters up to Ten Molecules

“…29 The NBO method provides a useful tool for exploring the nature of the HBs. 1,2,29 On the other hand, Bader's theory of atoms in molecules (AIM) 30 has been widely used in investigating or characterizing the properties at the HB bond critical points (BCPs). 1,[31][32][33][34][35][36][37] We employ the DFT, NBO, and AIM theories to study the optimized geometries, charge transfers, N‚‚‚H strengths, and N-H IR spectra of trans-diazene clusters up to 10 molecules and look at the origin of the noncooperativities in the clusters.…”

“…It has been reported [1][2][3][4] that, for most A-H‚‚‚B systems, an obvious contraction in H‚‚‚B (or elongation in A-H) with increased size of H-bonded systems is pervasive, which is regarded as an important signature of the cooperative effects in these systems. Different from the H-bonded systems, however, the linear trans-diazane clusters almost do not have cooperative effects in the geometric sense.…”

“…It has been extensively reported [1][2][3][4] that red shifts of the A-H stretching frequencies in the A-H‚‚‚B systems generally increase with the H-bonded cluster size; this is a reflection of cooperative effects. Therefore, the displacement in the hydride stretching frequency is always an indicator of the nature of cooperativity.…”

“…Most H-bonded A-H‚‚‚B systems exhibit so-called cooperative effects which reflect in marked contraction in the B‚‚‚H bonds (or elongation of the A-H bonds) and an obvious red shift of the A-H stretching frequencies. [1][2][3][4][5][6][7] However, in contrast to the general H-bonded systems, the linear trans-diazene clusters considered here hardly have the obvious cooperative effects.…”

Intermolecular perturbation in the self-assembly of melamine

“…It can be seen from Table 2a-d that in all complexes, as the number of CA monomers increases, the X•••A distance of the D-X•••A interactions increases linearly. This does not correspond with the cooperative effect of HBs and XBs interactions expected in self-assembly systems, i.e., X•••A distances decrease as the cluster size increases [45][46][47][48]. Thus, both energetic and geometrical criteria suggest a negative cooperativity of the interactions in these systems.…”