The Phase Transformation and Formation Mechanism of Isostructural Solvates: A Case Study of Azoxystrobin

Abstract

Azoxystrobin has one amorphous form and two solvent-free forms. A series of new solvates were obtained by crystallization experiments in 40 solvents. Among these solvates, four of them were successfully determined by single-crystal X-ray diffraction and analyzed in terms of molecular conformation, intermolecular interaction, and crystal-packing motifs. In addition, the physiochemical properties of all solvates were further studied and presented with comprehensive characterization. It was found that both properties and the size of solvent molecules attribute to the formation of isostructural azoxystrobin solvates. Isostructural solvates can be formed when the solvents have particular molecular size (molar volume ranging from 56.1 to 88.5 cm3/ mol) and solvent properties that could make weak interactions with azoxystrobin. Desolvation and formation mechanism of isostructural solvates were investigated through the phase transformations and crystal structure analysis. The desolvation of solvates first forms form B, then form B melts and recrystallizes into a stable form A. A possible mechanism for the formation of isostructural solvates was proposed.