Herein, a combined experimental–theoretical investigation of the subatomic structure of 1-(5-bromopyridin-2-yl)ethan-1-one in the crystal, the isolated molecule, and its dimer is presented. The use of novel structural descriptors—most of which are based on the conservative electronic force fields—provides an exceptional framework for elucidating chemical interactions in these systems within the conceptual contexts of Lewis acidity–basicity, interatomic electron transfer, and the concomitant manifestations of Fermi electron correlation in real space. The analysis of the vector fields relies extensively on the superposition of trajectory maps. The electron density gradient <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\nabla \rho (\mathbf{r})\)</EquationSource> </InlineEquation>, the electrostatic force field <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\mathbf{F}_{\mathrm{es}}(\mathbf{r})\)</EquationSource> </InlineEquation>, and the total static force field <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\mathcal{F}(\mathbf{r})\)</EquationSource> </InlineEquation> in the crystal, together with the distributions of the bosonic, fermionic, and total static potentials—<InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\varphi_{\mathrm{W}}(\mathbf{r})\)</EquationSource> </InlineEquation>, <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\varphi_{\mathrm{f}}(\mathbf{r})\)</EquationSource> </InlineEquation>, and <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\varphi_{\mathrm{em}}(\mathbf{r})\)</EquationSource> </InlineEquation>—are derived from the high-resolution single-crystal X-ray diffraction data and compared with theoretical results. Particular attention is devoted to the characterization of halogen bonding, nonclassical hydrogen bonding, and <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\pi\)</EquationSource> </InlineEquation>···<InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\pi\)</EquationSource> </InlineEquation> stacking in the crystal. To analyze the molecular association mediated by the Br···O=C halogen bond, in addition to the aforementioned properties, the exchange force field <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(\mathbf{F}_{x}(\mathbf{r})\)</EquationSource> </InlineEquation>, its component projection <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(\left[\mathbf{F}_{x}(\mathbf{r}) \cdot \mathcal{F}(\mathbf{r})\right]/|\mathcal{F}(\mathbf{r})|\)</EquationSource> </InlineEquation>, and the exchange charge density <InlineEquation ID="IEq13"> <EquationSource Format="TEX">\(\nabla \cdot \mathbf{F}_{x}(\mathbf{r})/(4\pi)\)</EquationSource> </InlineEquation> are employed as principal diagnostics. Importantly, for the Br···O=C halogen bond studied herein, the charge transfer is directed from the bromine atom acting as the Lewis acid to the oxygen atom acting as the Lewis base, rather than vice versa. Graphical Abstract

Anatomy and formation of Br···O=C halogen and nonclassical hydrogen bonds and \(\pi\)···\(\pi\) stacking: insights from the conservative electronic force fields in the molecular crystal and the supermolecule of 1-(5-bromopyridin-2-yl)ethan-1-one

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2026年3月21日

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Alina F. Saifina,
Sergey V. Kartashov,
Robert R. Fayzullin

摘要

Herein, a combined experimental–theoretical investigation of the subatomic structure of 1-(5-bromopyridin-2-yl)ethan-1-one in the crystal, the isolated molecule, and its dimer is presented. The use of novel structural descriptors—most of which are based on the conservative electronic force fields—provides an exceptional framework for elucidating chemical interactions in these systems within the conceptual contexts of Lewis acidity–basicity, interatomic electron transfer, and the concomitant manifestations of Fermi electron correlation in real space. The analysis of the vector fields relies extensively on the superposition of trajectory maps. The electron density gradient \(\nabla \rho (\mathbf{r})\) , the electrostatic force field \(\mathbf{F}_{\mathrm{es}}(\mathbf{r})\) , and the total static force field \(\mathcal{F}(\mathbf{r})\) in the crystal, together with the distributions of the bosonic, fermionic, and total static potentials— \(\varphi_{\mathrm{W}}(\mathbf{r})\) , \(\varphi_{\mathrm{f}}(\mathbf{r})\) , and \(\varphi_{\mathrm{em}}(\mathbf{r})\) —are derived from the high-resolution single-crystal X-ray diffraction data and compared with theoretical results. Particular attention is devoted to the characterization of halogen bonding, nonclassical hydrogen bonding, and \(\pi\) ··· \(\pi\) stacking in the crystal. To analyze the molecular association mediated by the Br···O=C halogen bond, in addition to the aforementioned properties, the exchange force field \(\mathbf{F}_{x}(\mathbf{r})\) , its component projection \(\left[\mathbf{F}_{x}(\mathbf{r}) \cdot \mathcal{F}(\mathbf{r})\right]/|\mathcal{F}(\mathbf{r})|\) , and the exchange charge density \(\nabla \cdot \mathbf{F}_{x}(\mathbf{r})/(4\pi)\) are employed as principal diagnostics. Importantly, for the Br···O=C halogen bond studied herein, the charge transfer is directed from the bromine atom acting as the Lewis acid to the oxygen atom acting as the Lewis base, rather than vice versa.

Graphical Abstract