Volume and Pressure Effects for Solvation: The Case Study on Polymorphs of Neat Triiodoimidazole Replaced by Its Solvate

Abstract

The formation of solvates in relation to the neat-crystal close-packing efficiency and the symmetry, involving the number of independent molecules (Z′), has been investigated. In the Cambridge Structural Database solvates are most frequent when the corresponding neat compounds have several independent molecules Z′ > 1. High pressure changes the energy difference between inequivalent molecules and their interactions, which can trigger phase transitions, solvation, multicomponent aggregation, and other transformations. When 2,4,5-triiodoimidazole (tIIm) polymorph α (Z′ = 3) was recrystallized above 0.2 GPa in methanol, a hemisolvate 2tIIm·CH3OH was obtained. Later, the hemisolvate could be obtained at normal conditions and then polymorphs α and β disappeared, and new syntheses and recrystallizations at 0.1 MPa yielded exclusively a new polymorph γ (Z′ = 4); when dissolved in methanol it precipitates as the methanol hemisolvate only. In its structure, chains of NH···N and NH···OH···N bonded molecules are for...