Polymorphism and structural diversities of LiClO4–β-alanine ionic co-crystals

Abstract

Three novel ionic co-crystals (ICCs) built from lithium perchlorate and β-alanine (LiClO₄·βAla, LiClO₄·2βAla-I, LiClO₄·2βAla-II) were obtained and structurally characterized. Crystals with a twofold excess of amino acid, LiClO₄·2βAla-I, were found to undergo a solvent-mediated phase transition, recrystallizing as the thermodynamically stable polymorph LiClO₄·2βAla-II. The transition was characterized by a series of PXRD measurements, observations performed under a microscope with polarized light and DSC experiments. Both polymorphs were found to exhibit virtually the same square-grid topology of lithium–alanine coordination sheets, yet they differ in symmetry and geometrical parameters of the networks. In the LiClO₄·βAla crystal structure, chain-like coordination polymers are formed. Responses to temperature change were determined for all three structures by performing a series of X-ray diffraction measurements in the 100–300 K range. Differences were elucidated with the help of a thermal tensor, which allowed us to identify the structural motifs most sensitive to temperature change.