Analysis of solvent-accessible voids and proton-coupled electron transfer of 2,6-bis(1H-imidazol-2-yl)pyridine and its hydrochloride

Abstract

The crystal structures of the solid form of solvated 2,6‐bis(1H‐imidazol‐2‐yl)pyridine (H2dimpy) trihydrate, C11H9N5·3H2O·[+solvent], I, and its hydrate hydrochloride salt 2‐[6‐(1H‐imidazol‐2‐yl)pyridin‐2‐yl]‐1H‐imidazol‐3‐ium chloride trihydrate, C11H10N5+·Cl−·3H2O, II, are reported and analysed in detail, along with potentiometric and spectrophotometric titrations for evaluation of the acid–base equilibria and proton‐coupled electron‐transfer reactions. Compound I crystallizes in the high‐symmetry trigonal space group P3221 with an atypical formation of solvent‐accessible voids, as a consequence of the 32 screw axis in the crystallographic c‐axis direction, which are probably occupied by uncharacterized disordered solvent molecules. Additionally, the trihydrated chloride salt crystallizes in the conventional monoclinic space group P21/c without the formation of solvent‐accessible voids. The acid–base equilibria of H2dimpy were studied by potentiometric and spectrophotometric titrations, and the results suggest the formation of H3dimpy+ (pKa1 = 5.40) and H4dimpy2+ (pKa2 = 3.98), with the electrochemical behaviour of these species showing two consecutive irreversible proton‐coupled electron‐transfer reactions. Density functional theory (DFT) calculations corroborate the interpretation of the experimental results and support the assignment of the electrochemical behaviour.

Role of Protonation and Isomerism in the Supramolecular Architectures of Heteroaryl-2-imidazole Compounds: Crystal Packing Patterns and Energetics

“…We were not able to isolate the monoprotonated crystal structure (H 2 impyCl). Contrary to what was observed for a similar molecule 2,6-bis­(1 H -imidazol-2-yl)-pyridine, our results for Himpy showed that the p K a for the imidazolium species (5.50) was much higher than for the pyridinium one (second protonation takes place below pH 1) so the best possible reason for the lack of success in the crystallization is the instability of this species (see further in the text) and not the difference between p K a values in this case (Figure S21 and Table S2). The geometric parameters of the imi ring feature for the bond angle values of C2–N1–C5: 107.70(2)° and C2–N3–C4: 108.87(2)°, which clearly depicts the protonation of this ring.…”

“…19 Several works explore intermolecular interactions of imidazolium-containing compounds with carboxylic acids, 20 halogens, 21 and metal ions, 22 providing a huge diversity of supramolecular assemblies for different purposes such as crystal engineering, 23 organic−inorganic hybrid ferroelectric materials, 24 and ionic liquid compounds. 25 Systematic studies of crystal structures of neutral heteroaryl imidazole-containing compounds, as well as their protonated forms and their supramolecular arrangement patterns, are scarce in the literature 26 even in reputable databases such as the Cambridge Crystallographic Data Centre. One rare example is the work using heteroaryl-2-imidazole molecules which were cocrystallized along with halogen-containing molecules to assess the competition between halogen-bond interactions and hydrogenbond interactions in the assembly of the supramolecular network.…”

Molecular Insights into Water–Chloride and Water–Water Interactions in the Supramolecular Architecture of Aconine Hydrochloride Dihydrate

“…Likewise, the Hirshfeld surfaces of six water molecules exhibit anomalous behaviors, as anticipated due to the presence of short contacts (Figure a–f). Comparable observations have been reported in the case of 2,6-bis­(1H-imidazol-2-yl) pyridine hydrochloride trihydrate . The d norm surface vividly depicts the regions where hydrogen bonding interactions involving the O and H atoms occur, which are visually emphasized by red spots.…”

“…Comparable observations have been reported in the case of 2,6-bis(1H-imidazol-2-yl) pyridine hydrochloride trihydrate. 42 The d norm surface vividly depicts the regions where hydrogen bonding interactions involving the O and H atoms occur, which are visually emphasized by red spots. The participation of all water molecules in these H···O contacts can be classified into three distinct groups: the first group encompasses interactions between water molecules and cations (H 2 O1 and MC; H 2 O2 and MA; H 2 O2 and MB; H 2 O5 and MA; H 2 O5 and MB); the second group comprises interactions between water molecules themselves as well as cation (H 2 O4 and H 2 O3; H 2 O4 and MB); and the third group solely involves interactions between water molecules themselves (H 2 O3 and H 2 O4; H 2 O3 and H 2 O6).…”

Water oxidation catalysts based on Ru(II) and Cu(II) complexes containing pyridinic-imidazole ligands and photocatalytic hydrogen evolution reaction using RuNPs@TiO2

“…[57,63,64,79,80] Further characterization details (COSY, UV-Vis, DSC,Emission spectra, FTIR, etc.) are not shown in this thesis and can be found in the published paper (ref [81]…”