The Role of Lattice Matching Techniques in the Characterization of Polymorphic Forms

TL;DR

This paper discusses how lattice matching techniques can help identify and characterize different polymorphic forms of materials, which is important for ensuring correct drug development and material science applications.

Contribution

The paper introduces and applies lattice-matching techniques to detect and validate polymorphic forms, preventing misidentification in crystallography.

Findings

Lattice-matching techniques can identify new polymorphic forms.

These methods can reveal missed symmetry or lattice relationships that prevent incorrect structure determination.

The techniques are recommended for integration into the editorial review process of crystallography journals.

Abstract

An inspection of the recent literature reveals that polymorphism is a frequently encountered phenomenon. The recognition of polymorphic forms plays a vital role in the materials sciences because such structures are characterized by different crystal packing and accordingly have different physical properties. In the pharmaceutical industry, recognition of polymorphic forms can be critical for, in certain cases, a polymorphic form of a drug may be an ineffective therapeutic agent due to its unfavorable physical properties. A check of the recent literature has revealed that in some cases new polymorphic forms are not recognized. In other instances, a supposedly new polymeric form is actually the result of an incorrect structure determination. Fortunately, lattice-matching techniques, which have proved invaluable in the identification and characterization of crystal structures, represent a powerful tool for analyzing polymorphic forms. These lattice-matching methods are based on either of two strategies: (a) the reduced cell strategy–the matching of reduced cells of the respective lattices or (b) the matrix strategy–the determination of a matrix or matrices relating the two lattices coupled with an analysis of the matrix elements. Herein, these techniques are applied to three typical cases–(a) the identification of a new polymorphic form, (b) the demonstration that a substance may not be a new polymorphic form due to missed symmetry, and (c) the evaluation of pseudo polymorphism because of a missed lattice. To identify new polymorphic forms and to prevent errors, it is recommended that these lattice matching techniques become an integral part of the editorial review process of crystallography journals.