Structural transformation of pyridinium iodide proceeding in the solid state

Abstract

Co-grinding of 1-(2-oxo-2-phenylethyl)-pyridinium iodide (Py⁺·I⁻, 1) with 0.5 equivalent of I₂ affords the mixture of 1 and Py⁺·I₃⁻ (3) soon after grinding. The resultant powder gradually converts to a double salt, Py⁺·(I⁻)_0.5·(I₃⁻)_0.5 (2), by leaving it at ambient temperature for one month. To clarify the mechanism of this “self-assembly” behavior in the solid state, mechanochemical reactions at various 1 : I₂ ratios (1 : I₂ = 1 : 0.1, 1 : 0.2, 1 : 0.4, 1 : 0.6, 1 : 0.8, 1 : 1, and 1 : 2) have been examined. Comparison of these studies indicates that cations and anions spontaneously diffuse and rearrange in the solid state following the anion change from I⁻ to I₃⁻.