A QTAIM and stress tensor perspective of large-amplitude motions of the tetrasulfur tetranitride S₄N₄molecular graph

Abstract

The nature of the bonding interactions including the intramolecular SAS interactions in tetrasulfur tetranitride, S 4 N 4 are probed by performing very large amplitude vibrations of all of the 18 normal modes of vibration. The QTAIM and stress tensor point properties are -then investigated and found to be highly dependent on the mode of vibration. A considerable degree of metallicity n(r b ) is found for the SAS and SAN bonding interactions. A unique bonding feature is found for a small amplitude vibration of the most anharmonic mode of this investigation, mode 2, where the SAS bond critical point (BCP) transforms from a closed-shell SAS BCP to a shared-shell SAS BCP. We find 17 new unique QTAIM topologies for the molecular graphs corresponding to the 18 modes of vibration along with seven "missing" topologies that are mapped onto a spanning 2-D Quantum topology Phase Diagram (QTPD). In addition, eleven unique topologies existing on 3-D QTPDs are found due to the presence of non-nuclear attractors (NNAs). We use the stress tensor eigenvalues to explain the invariance of the numbers and types of QTAIM critical points. The applicability of both the stiffness S and stress tensor stiffness S r are also explored. Two new bond measures are introduced, a polarizability P and the stress tensor polarizability P r which are derived from the stiffness S and stress tensor stiffness S r , respectively.

A stress tensor and QTAIM perspective on the substituent effects of biphenyl subjected to torsion

“…Previously, it was also found that the stress tensor stiffness, S σ produced results that were in line with physical intuition for a bond‐path undergoing torsion, in contrast with those from the QTAIM stiffness, S . Smaller values of the stress tensor stiffness S σ indicate the dominance of the tensile eigenvalue λ 3 σ compared with λ 1 σ which is the compressive and therefore corresponds to greater bond‐path polarizabilities P σ = | λ 3 σ |/| λ 1 σ | . Higher values of the stress tensor polarizability P σ will correlate with lower values of the stress tensor stiffness S σ and also with longer bond‐path‐lengths.…”

“…Smaller values of the stress tensor stiffness S r indicate the dominance of the tensile eigenvalue k 3r compared with k 1r which is the compressive and therefore corresponds to greater bond-path polarizabilities P r 5 |k 3r |/|k 1r |. [42] Higher values of the stress tensor polarizability P r will correlate with lower values of the stress tensor stiffness S r and also with longer bond-path-lengths. Longer bondpaths would be expected to correlate with more topologically unstable less negative values of the total local energy density H(r b ) and therefore greater topological instabilities of a BCP.…”

A vector‐based representation of the chemical bond for predicting competitive and noncompetitive torquoselectivity of thermal ring‐opening reactions

“…Previously, the stress tensor polarizability P σ = | λ 3σ |/| λ 1σ | was defined as the reciprocal of the stress tensor stiffness S σ . Larger values of the stress tensor polarizability P σ indicate the dominance of the tensile eigenvalue λ 3σ compared λ 1σ which is the compressive and, therefore, corresponds to larger bond‐path P σ = | λ 3σ |/| λ 1σ |.…”

Neutral binary chalcogen–nitrogen and ternary S,N,P molecules: new structures, bonding insights and potential applications

“…In particular, considerable metallic behaviour was apparent in the S-S bond critical points for all modes. 17 The experimental implications of this finding are yet to be investigated.…”

“…A different aspect of the bonding interactions in 1 (E = S) was reported in 2016 by Jenkins and co-workers. 17 By applying QTAIM (quantum theory of atoms in molecules) methodology to all 18 modes of vibration of the cage molecule, these authors found a considerable degree of metallicity in the S-S and S-N bonding interactions, on the basis of the delocalisation of the electron density away from the atoms. In particular, considerable metallic behaviour was apparent in the S-S bond critical points for all modes.…”