Two New Organic Co-Crystals Based on Acetamidophenol Molecules

Iryna Andrusenko,Jason Potticary,Joseph Hitchen,Simon R Hall,Enrico Mugnaioli,Mauro Gemmi

doi:10.3390/sym14030431

Iryna Andrusenko, Jason Potticary + Show 4 more

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https://doi.org/10.3390/sym14030431

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Abstract

Herein we present two new organic co-crystals obtained through a simple solution growth process based on an acetamidophenol molecule, either paracetamol or metacetamol, and on 7,7,8,8-tetracyanoquinodimethane (TCNQ). These co-crystals are part of a family of potential organic charge transfer complexes, where the acetamidophenol molecule behaves as an electron donor and TCNQ behaves as an electron acceptor. Due to the sub-micron size of the crystalline domains, 3D electron diffraction was employed for the structure characterization of both systems. Paracetamol-TCNQ structure was solved by standard direct methods, while the analysis of metacetamol-TCNQ was complicated by the low resolution of the available diffraction data and by the low symmetry of the system. The structure determination of metacetamol-TCNQ was eventually achieved after merging two data sets and combining direct methods with simulated annealing. Our study reveals that both paracetamol-TCNQ and metacetamol-TCNQ systems crystallize in a 1:1 stoichiometry, assembling in a mixed-stack configuration and adopting a non-centrosymmetric P1 symmetry. It appears that paracetamol and metacetamol do not form a strong structural scaffold based on hydrogen bonding, as previously observed for orthocetamol-TCNQ and orthocetamol-TCNB (1,2,4,5-tetracyanobenzene) co-crystals.

Highlights

Symmetry is the true heart of crystallography
Such platelets are agglomerates of much smaller crystalline domains, and this hinders the possibility of single-crystal X-ray diffraction experiments
A close look at 3D ED reconstructions revealed no hint of extinction features (Figure 3a–c)

Summary

Introduction

Symmetry is the true heart of crystallography. It is because of the symmetry that the description of a crystal passes from an Avogadro number of atoms to few atoms in the asymmetric unit. This simplifies enormously the problem of solving the crystal structure of an unknown phase. When the crystals become extremely small, in the range of few nanometers, the problem of symmetry determination becomes extremely challenging. The beautiful hints given by the crystal shape are hard to recognize in electron microscopy images of nanocrystals. The guide given by single-crystal diffraction data is not available when the size falls below a few microns.

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