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The nature of π-hole interactions between iodide anions and quinoid rings in the crystalline state.

ABSTRACT: The investigated co-crystal of 3-chloro-N-methylpyridinium iodide with tetrabromoquinone (3-Cl-N-MePy·I·Br₄Q) reveals a π-hole interaction between an iodide anion and a quinoid ring involving an n → π* charge transfer. The quinoid ring has a partial negative charge (estimated to be in the range 0.08-0.11e) and a partial radical character, which is related to the black colour of the crystals (crystals of neutral tetrabromoquinone are yellow). A detailed X-ray charge density study revealed two symmetry-independent bond critical points between the iodide anions and carbon atoms of the ring. Their maximum electron density of 0.065 e Å^-3 was reproduced by quantum chemical modelling. The energy of the interaction is estimated to be -11.16 kcal mol^-1, which is comparable to the strength of moderate hydrogen bonding (about -10 kcal mol^-1); it is dominantly electrostatic in nature, with a considerable dispersion component.

SUBMITTER: Milasinovic V

PROVIDER: S-EPMC9980391 | biostudies-literature | 2023 Mar

REPOSITORIES: biostudies-literature

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The nature of π-hole interactions between iodide anions and quinoid rings in the crystalline state.

Milašinović Valentina V Vuković Vedran V Krawczuk Anna A Molčanov Krešimir K Hennig Christoph C Bodensteiner Michael M

IUCrJ 20230301 Pt 2

The investigated co-crystal of 3-chloro-N-methylpyridinium iodide with tetrabromoquinone (3-Cl-N-MePy·I·Br<sub>4</sub>Q) reveals a π-hole interaction between an iodide anion and a quinoid ring involving an n → π* charge transfer. The quinoid ring has a partial negative charge (estimated to be in the range 0.08-0.11e) and a partial radical character, which is related to the black colour of the crystals (crystals of neutral tetrabromoquinone are yellow). A detailed X-ray charge density study revea ...[more]

PMID: 36692857

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Project description:Despite the technological importance of urea perhydrate (percarbamide) and sodium percarbonate, and the growing technological attention to solid forms of peroxide, fewer than 45 peroxosolvates were known by 2000. However, recent advances in X-ray diffractometers more than tripled the number of structurally characterized peroxosolvates over the last 20 years, and even more so, allowed energetic interpretation and gleaning deeper insight into peroxosolvate stability. To date, 134 crystalline peroxosolvates have been structurally resolved providing sufficient insight to justify a first review article on the subject. In the first chapter of the review, a comprehensive analysis of the structural databases is carried out revealing the nature of the co-former in crystalline peroxosolvates. In the majority of cases, the coformers can be classified into three groups: (1) salts of inorganic and carboxylic acids; (2) amino acids, peptides, and related zwitterions; and (3) molecular compounds with a lone electron pair on nitrogen and/or oxygen atoms. The second chapter of the review is devoted to H-bonding in peroxosolvates. The database search and energy statistics revealed the importance of intermolecular hydrogen bonds (H-bonds) which play a structure-directing role in the considered crystals. H2O2 always forms two H-bonds as a proton donor, the energy of which is higher than the energy of analogous H-bonds existing in isostructural crystalline hydrates. This phenomenon is due to the higher acidity of H2O2 compared to water and the conformational mobility of H2O2. The dihedral angle H-O-O-H varies from 20 to 180° in crystalline peroxosolvates. As a result, infinite H-bonded 1D chain clusters are formed, consisting of H2O2 molecules, H2O2 and water molecules, and H2O2 and halogen anions. H2O2 can form up to four H-bonds as a proton acceptor. The third chapter of the review is devoted to energetic computations and in particular density functional theory with periodic boundary conditions. The approaches are considered in detail, allowing one to obtain the H-bond energies in crystals. DFT computations provide deeper insight into the stability of peroxosolvates and explain why percarbamide and sodium percarbonate are stable to H2O2/H2O isomorphic transformations. The review ends with a description of the main modern trends in the synthesis of crystalline peroxosolvates, in particular, the production of peroxosolvates of high-energy compounds and mixed pharmaceutical forms with antiseptic and analgesic effects.

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The nature of π-hole interactions between iodide anions and quinoid rings in the crystalline state.

Publications

The nature of π-hole interactions between iodide anions and quinoid rings in the crystalline state.

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