Stereochemistry and Twisted Crystals

Catherine E Killalea,David B Amabilino

doi:10.1002/ijch.202100063

Abstract

AbstractThis review article discusses a link between stereochemistry and structural and morphological chirality. We present the remarkably frequent, but less often reported, growth of twisted crystals and discuss the reasons for their formation and ways to favor their growth. The more commonly encountered conglomerates and racemic compounds can be formed by achiral molecules, but the emergence of morphological chirality is often not considered in this context and perhaps deserves attention. Twisted crystals are known for a wide variety of materials, molecular and macromolecular, complexes and oxides, and so on. In growing crystals, twisting of lamellae because of strain generated during growth eventually unwinds in larger objects, and may not be detected. This kind of chiral morphology arising from low symmetry growth, and the challenges and opportunities for research in the area, are highlighted. In particular, the link between structural bending in supramolecular aggregates in solution or at interfaces, chiral nanofilaments in liquid crystals, and chiral polymers, is discussed.

Highlights

The famous enantiomorphic crystals formed by sodium ammonium tartrate[1,2] are visibly chiral
Molecular chirality is not essential for the formation of enantiomorphic crystals, not even that forced by spontaneous resolution of achiral components to give chiral structures: Chiral morphologies emerge in the growth of otherwise achiral chemistry
We aim to show here that while a twisted crystal might be considered an inconvenience for the scientist wishing to obtain a single crystal structure, the emergence of these exotic and beautiful morphologies raises fascinating challenges

Summary

Introduction

The famous enantiomorphic crystals formed by sodium ammonium tartrate[1,2] are visibly chiral. Molecular chirality is not essential for the formation of enantiomorphic crystals, not even that forced by spontaneous resolution of achiral components to give chiral structures: Chiral morphologies emerge in the growth of otherwise achiral chemistry This formation of twisted crystals was recognized in the 19th century (Figure 1).[17] Many examples were discovered and highlighted along with more contemporary discoveries in a review on twisted and bending merging in crystal growth.[18] twisting in crystal growth is proving to be a frequent phenomenon under certain conditions.[19] We aim to show here that while a twisted crystal might be considered an inconvenience for the scientist wishing to obtain a single crystal structure, the emergence of these exotic and beautiful morphologies raises fascinating challenges. These techniques give hints to answer the key questions in these systems, how and why does twisting occur?

Explaining twisting during crystal growth

Findings

Making twisted crystals