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

摘要

The crystal structures of the solid form of solvated 2,6‐bis(1 H ‐imidazol‐2‐yl)pyridine (H 2 dimpy) trihydrate, C 11 H 9 N 5 ·3H 2 O·[+solvent], I , and its hydrate hydrochloride salt 2‐[6‐(1 H ‐imidazol‐2‐yl)pyridin‐2‐yl]‐1 H ‐imidazol‐3‐ium chloride trihydrate, C 11 H 10 N 5 + ·Cl ? ·3H 2 O, 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 P 3 2 21 with an atypical formation of solvent‐accessible voids, as a consequence of the 3 2 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 P 2 1 / c without the formation of solvent‐accessible voids. The acid–base equilibria of H 2 dimpy were studied by potentiometric and spectrophotometric titrations, and the results suggest the formation of H 3 dimpy + (p K a1 = 5.40) and H 4 dimpy 2+ (p K a2 = 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.