A Bond Path and an Attractive Ehrenfest Force Do Not Necessarily Indicate Bonding Interactions: Case Study on M₂X₂(M=Li, Na, K; X=H, OH, F, Cl)

Abstract

Interactions in dimers of model alkali metal derivatives M(2)X(2) (M = Li or Na or K; X = H or F, Cl, OH) are studied in the frame of the quantum theory of atoms in molecules (QTAIM) using the interacting quantum atoms approach (IQA). Contrary to opinion prevalent in QTAIM studies, the interaction between two anions linked by a bond path is demonstrated to be strongly repulsive. One may therefore say that a bond path does not necessarily indicate bonding interactions. The interactions between two anions or two cations that are not linked by a bond path are also strongly repulsive. The repulsive anion-anion and cation-cation interactions are outweighed by much stronger attractive anion-cation interactions, and the model molecules are therefore in a stable state. The attractive Ehrenfest forces (calculated in the frame of the QTAIM) acting across interatomic surfaces shared by anions in the dimers do not reflect the repulsive interactions between anions. Probable reasons of this disagreement are discussed. The force exerted on the nucleus and the electrons of a particular atom by the nucleus and the electrons of any another atom in question is proposed. It is assumed that this force unambiguously exposes whether basins of two atoms are attracted or repelled by each other in a polyatomic molecule.

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

“…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].…”

IQA-embedded fragment attributed molecular system energy change in exploring intramolecular interactions

“…To asses reliability of B3LYP data we compared the sums of halved interaction energies,   A X AX int 0.5E , because this energy term (i) involves contributions coming from interactions with all atoms in a molecule and (ii) is always generated for any atom selected for the IQA calculations, hence it 27 was also available at the MP2 level. Relevant data obtained for representative atoms of the bay at both levels of theory are presented in Table 7 (a full B3LYP data set is included in Table S13 in the SI).…”

“…However, besides classical H-bonds, there are different intramolecular interactions which might be either of stabilizing or destabilizing nature even when a BP is observed. This is because the local diatomic interaction might be overall destabilizing [22][23][24][25][26][27][28] when, e.g., electrostatic term of the interaction dominates and is of repulsive nature. Recently, a Non-covalent Interaction (NCI) method [29][30][31] (it is making use of the reduced density gradient which, in density functional theory, describes the deviation from a homogeneous electron distribution) was proposed to identify intramolecular 'attractive' (density accumulation) and 'repulsive' (density depletion) interactions.…”

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

“…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)…”