Abstract
cis-4,4'-(Diazenediyl)bis(2,3,5,6-tetrafluorobenzoic acid), C14H2F8N2O4, and its ethanol disolvate, C14H2F8N2O4·2C2H5OH, represent new examples of self-stabilized cis-configured azo-benzenes obtained by a common crystallization procedure at room temperature under normal laboratory lighting conditions. The target structure constitutes of two 2,3,5,6-tetra-fluoro-benzoic acid residues linked to each other by a cis-configured azo group and was confirmed for two isolated specimens extracted from the same sample, corresponding to a solvent-free form and an ethanol disolvate. In the solvent-free form, the mol-ecule is characterized by rotational symmetry around a twofold rotation axis bis-ecting its central N=N bond while this symmetry is not present in the solvated form. The values of the inclination angles of the terminal carboxyl groups towards the corresponding benzene rings vary from 5.2 (4) to 45.7 (2)°, depending on the crystal composition. In the unsolvated form, the mol-ecules are linked through identical hydrogen bonds with a classical R 2 2(8) graph-set ring motif of carb-oxy-lic acids, by generating supra-molecular chains running approximately parallel to [101]. The presence of ethanol in the solvated form also leads to changes in the short-contact pattern to produce both the R 4 4(12) ring and open-chain motifs with alternating alcohol and di-carb-oxy-lic acid mol-ecules.
Highlights
In the solvent-free form, the molecule is characterized by rotational symmetry around a twofold rotation axis bisecting its central N N bond while this symmetry is not present in the solvated form
The parent structure of azobenzene and its numerous differently substituted derivatives is comprised of two aromatic benzene rings separated by an azo group
We report the crystal structures of 4,40(diazenediyl)bis(2,3,5,6-tetrafluorobenzoic acid) with (I) and without residual ethanol (II), both adopting the cis configuration during a common crystallization procedure from the same solution in ethanol at room temperature under normal laboratory lighting conditions
Summary
The parent structure of azobenzene and its numerous differently substituted derivatives is comprised of two aromatic benzene rings separated by an azo group. Such controlled trans-cis interconversions at the molecular scale, typically performed on the microsecond time interval or faster, have been amplified successfully to a macroscopic material photomechanical response, suggesting a highly promising route toward creating and applying diverse photoresponsive systems (Mahimwalla et al, 2012; Bushuyev et al, 2018) In this context, azobenzenes, capable of adopting long-term stabilized cis-forms, represent an important tool for studying the trans–cis isomerization mechanisms, as well as for tuning the photomechanical properties. We report the crystal structures of 4,40(diazenediyl)bis(2,3,5,6-tetrafluorobenzoic acid) with (I) and without residual ethanol (II), both adopting the cis configuration during a common crystallization procedure from the same solution in ethanol at room temperature under normal laboratory lighting conditions
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