London Dispersion Forces in Crystal Packing of Thiourea Derivatives

Abstract

Novel thioureas RNHC­(S)­NHP­(S)­(OiPr)2 [R = (HOCH2)­(Me)2C (1), Me2CH2CH2 (2), 2-CF3C6H4 (3), 2-Pym (4), and bis-thiourea 1,5-C10H6{NHC­(S)­NHP­(S)­(OiPr)2} (5)] have been synthesized and characterized by NMR, X-ray diffraction, Hirshfeld surface analysis, and theoretical ETS-NOCV charge and energy decomposition calculations. The monomers contain multiple intramolecular noncovalent interactions including N–H···X (X = O, 1–3; F, 3; N, 4; S, 5) and C–H···Y (Y = O, 1; N, 2 and 3; S, 4 and 5) augmented further by homopolar C–H···H–C contacts in all the structures. It has been determined that the three-dimensional crystal networks are primarily constituted from intermolecular H···H and H···S contacts due to homopolar C–H···H–C as well as X–H···S (X = N, C) interactions. They are, depending on the system, augmented further by C–H···Y (Y = π, S, F) as well as by σ-hole­(S)···π interactions. ETS-NOCV allowed us to delineate that in the case of C–H···H–C, C–H···Y, and σ-hole­(S)···π intermolecular interactions, except for the electrostatically dominated N–H···N in 4, London dispersion forces appeared to be a crucial contributor to the stability with non-negligible factors stemming from electrostatics and charge delocalization terms. Remarkably, the dispersion dominated (∼50% of the overall stabilization ΔE elstat + ΔE orb + ΔE dispersion) σ-hole­(S)···π interactions appeared to be the strongest among all the discovered interactions, including classical hydrogen bonds N–H···N. The electrostatic and charge delocalization contributions within the σ-hole­(S)···π interactions amount to ∼30% and ∼20%, respectively.

Formation of active species from ruthenium alkylidene catalysts—an insight from computational perspective

“…Particularly, ΔE dispersion is extremely significant at absolute level; it is −141 kJ mol −1 for 2 and − 144 kJ mol −1 for 1 ( Table 2). It is in accord with the recent findings which highlight that bulky substituents might lead to enhancement of the molecular stability since their London dispersion donating properties might easily outweigh the corresponding steric (Pauli/kinetic) repulsion [59][60][61][62][63][64]. In the forthcoming paragraphs, electron density reorganization channels due to formation of various types of non-covalent interactions are identified and discussed in detail.…”

“…The former involves charge transfer from the lone pair of chlorine to the empty σ*(C-H), whereas the latter consist of donation from σ(C-H) to the empty π* of phenyl ring. Additionally, homopolar dihydrogen close contacts CH … HC lead to the two ways charge delocalization channels σ(C-H)➔ σ*(C-H) (and vice-versa) [61][62][63][64]. They all amount to ΔE orb (4 + 5 + 6) = −14 kJ mol −1 (Fig.…”

Structural versatility of the quasi-aromatic Möbius type zinc(ii)-pseudohalide complexes – experimental and theoretical investigations

“…The prevalence of the DE disp term is consistent with recent ndings, which rediscover the importance of London dispersion forces in small and sizeable species. 24,27,[40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] In 3 the [Zn(NCS) 4 ] 2À anion sticks very strongly (DE int ¼ À193.21 kcal mol À1 ) to two neighboring stacked [Zn(NCS)L II ] + units primarily through electrostatic forces (75.3% of the overall stabilization) (Fig. 5).…”

“…In order to evaluate aromaticity in 1-3, we have applied the electron density of delocalized bonds (EDDB) method, which has been proposed to visualize and quantify aromaticity and chemical resonance in a wide range of chemical species. [57][58][59][60] Moreover, it has recently been shown that, in the case of organometallics, the EDDB method provides very useful data on the role of the transition metal d-orbitals in electron delocalization, 24,27,50,61 which is inaccessible by means of such popular and commonly used aromaticity descriptors as the nucleusindependent chemical shi (NICS) 62 or the anisotropy of the induced current density (ACID). 63 The global EDDB isocontours and the corresponding electron populations of 1-3 are collected in Fig.…”

“…7). It demonstrates the two-folded role of bulky substituents: they are not only dispersion donors, [40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] but they also lead to amplication of the 7-MR twist (and enhanced quasiaromaticity). Previously only the former feature has been recognized.…”