Contribution of Different Crystal Packing Forces in π-Stacking: From Noncovalent to Covalent Multicentric Bonding

Abstract

The present review is aimed to compare crystal packing interactions contributing to stacking arrangements of primarily nonaromatic systems referring only briefly to classical aromatic stacking. The classical aromatic stacking is mainly based on weak dispersion interactions (E ≤ 1 kcal mol–1) whereas heteroaromatics reveal more electrostatic (or specifically dipolar) contributions (E = 5–10 kcal mol–1). Based mainly on our charge density studies and DFT calculations, the results show that (i) all planar rings stack, regardless of aromaticity (or delocalization of π electrons) and (ii) stacking interactions cover a wide continuum ranging from weak, mainly dispersion interactions (E < 5 kcal mol–1) to unlocalized two-electron multicentric (2e/mc) covalent bonds (“pancake bonds”, E > 15 kcal mol–1). Our recent studies showed that quinones form face-to-face stacks and the energies of interactions exceed 10 kcal mol–1; ours and other authors’ results indicate that interactions between planar radicals involve a significant contribution of covalent bonding. Thus, π-interactions cover a broad range of energies, ranging from ≤1 to ≥20 kcal mol–1, and the interactions span from weak dispersion to multicentric covalent bonding. Therefore, development of a universal model of stacking is needed. In this respect, stacking can be compared to hydrogen bonding, which also ranges between dispersion (weakest hydrogen bonds, such as C–H···S and C–H···Cl) and two-electron/three-centric covalent bonding (the strongest “symmetrical” hydrogen bonds).

Interplay of π-stacking and inter-stacking interactions in two-component crystals of neutral closed-shell aromatic compounds: periodic DFT study

“…The obtained results are in general agreement with the literature data. 17,40 IMIs between innite stacks are called as inter-stacking. In the considered crystals, an electron-decient molecule from a given stack is surrounded by electron-rich molecules from neighboring stacks and vice versa ( Fig.…”

“…39 Obviously, the electrostatic contribution to the pstacking energy in such systems is caused by interactions of various types (Coulomb, dipole-dipole, etc.). 40 There are numerous two-component (binary) crystals composed of two organic compounds unable to form conventional hydrogen bonding. 5,6,29,30,34 The association modes mostly include stacking of at systems, one of them usually being an aromatic hydrocarbon, e.g.…”

Pressure‐Induced Conversion of a Paramagnetic FeCo Complex into a Molecular Magnetic Switch with Tuneable Hysteresis

“…Such interactions are not as well known as classical π‐interactions, but they can show higher stacking energy of ca. 10–20 kcal mol −1 . In the case of vbik1, these interactions are combined with an antiparallel arrangement of two C=O groups in close contact, which build an additional dipolar interaction whose energy values are similar to those of H‐bonds .…”

“…10–20 kcal mol −1 . In the case of vbik1, these interactions are combined with an antiparallel arrangement of two C=O groups in close contact, which build an additional dipolar interaction whose energy values are similar to those of H‐bonds . Upon applied pressure, as the distances decrease (see SI), one would expect that the dominant electrostatic interactions are reinforced, leading to the enhancement of the elastic interactions that is responsible for the unusual pressure‐induced bistability observed in 1 .…”

Anion Influence on the Packing of 1,3-Bis(4-Ethynyl-3-Iodopyridinium)-Benzene Halogen Bond Receptors

“…Taken together, we see that small changes in the arylethynyl scaffolds can lead to slightly different packing. However, dimer or slip-stack packing is persistent, suggesting that the larger cation and π-π interactions significantly influence the resulting solid-state packing [64]. Also, the frequency of anions supporting the formation of dimers by accepting contacts from each unit of the dimer highlights its common role as a building unit.…”