Evaluating common QTAIM and NCI interpretations of the electron density concentration through IQA interaction energies and 1D cross-sections of the electron and deformation density distributions

Abstract

Highlights• Classical steric clashes might have the same topological features as bonding interactions.• An AIL can be observed for highly attractive or repulsive interactions.• An AIL might be a result of either an inflow or outflow of density.• Locally accumulated density does not imply an attractive interaction or an inflow of density.• Nature of an interaction can change with molecular environment. Graphical abstract 2 AbstractNine kinds of inter-and intramolecular interactions were investigated by exploring the topology of electron density in the interatomic regions using standard protocols of QTAIM, IQA and NCI techniques as well as in-house developed cross-sections of the electron and deformation density distributions. The first four methods provide the properties of the resultant density distribution in a molecular system whereas the later illustrates the process, inflow or outflow of density from fragments to the interatomic region of an interaction on its formation in a molecular system. We used (i) the QTAIM-defined atomic interaction line, AIL (presence or absence), (ii) IQA-defined interaction energy, attractive to repulsive, (ii)  2 < 0 to  2 >0, or (iii) (r) > 0 to (r) < 0; hence, none of the topological indices used here, either separately or combined, can be used to definitely predict the (de)stabilizing nature of an interaction except highly repulsive ones for which the absence of AIL, interatomic density depletion and outflow of density on interaction formation are observed.

Non-Covalent Interactions in Hydrogen Storage Materials LiN(CH3)2BH3 and KN(CH3)2BH3

“…It is probably important to add that the electron density accumulation in the inter-hydrogen region of BH¨¨¨HB is indeed sufficient to observe a bond path (as it has been noted by McGrady et al [29])-however, it does not necessarily imply the overall stabilizing interactions: for example, as nicely demonstrated by Cukrowski et al [36], two water molecules enforced to approach each other via oxygen atoms leads to formation of the oxygen-oxygen bond critical point, however, the overall binding energy is as expected positive (destabilizing) due to the fact that some subtle stabilization arising from the electron-exchange channel (resulting also in the negative ∆E orb values) is diminished by the Pauli and electrostatic repulsion. A similar situation is observed in dimers of M 2 X 2 (for M = Li, K, X = H, Cl) where M-X stabilization outweighs the repulsion stemming from M-M and X-X interactions [73].…”

“…It is noteworthy that these types of connections are intuitively considered as destabilizing due to the lack of electrostatic attraction between hydrogen atoms-homopolar dihydrogen interactions (especially the intramolecular ones) are still a matter of debate in the literature [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Very recently more and more evidence has been reported in the literature that highlight the stabilizing nature of homopolar dihydrogen interactions [17,21,29,[36][37][38][39][40][41][42][43][44][45][46]. Accordingly, in this work we provide complementary results which shed light on energetic, quantitative and qualitative characteristics of non-covalent interactions that contribute to the stability of LiN(CH3)2BH3 and KN(CH3)2BH3 crystals.…”

“…Accordingly, in this work we provide complementary results which shed light on energetic, quantitative and qualitative characteristics of non-covalent interactions that contribute to the stability of LiN(CH3)2BH3 and KN(CH3)2BH3 crystals. It is an important goal as it is known that purely topological QTAIM analysis might provide bond paths between atoms (or fragments) even in situations where the overall interaction energies are positive (destabilizing) [36]. Therefore, we applied the charge and energy decomposition scheme (ETS-NOCV) [47][48][49] which has been proven to provide compact, qualitative and quantitative, descriptions of various types of chemical bonds starting from strong covalent bonds, going through dative connections [47][48][49] and ending up at various non-covalent interactions [7,8,37,50,51].…”

Structural-topological preferences and protonation sequence of aliphatic polyamines: a theoretical case study of tetramine trien

“…It is then most interesting to note that indeed, as one would expect due to the presence of AIL, a blue isosurface is observed between these two N-atoms but, most surprisingly, it is not surrounded by red-coloured area. The blue in the centre and red on the outskirts discs are synonymous with strain caused by crowded atomic environment and have been reported for, e.g., water dimer where d(O,H) of intermolecular interaction was smaller than that at the equilibrium [40] or for water dimer with forced-to-be Oatoms in close proximity [34]. There is another important observation to be made.…”

“…An analysis of Tables S3-S6 in neglected. Furthermore, since the  CP value of an interaction does not necessarily give sufficient information as to the stabilizing or otherwise nature of an interaction [34][35][36][37], we therefore decided to gain further insight from the recently developed non covalent interaction index (NCI)…”