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Title: Portrayal of the Color Polymorphism in the 5-Acetyl-derivative of ROY
Authors: Nogueira, Bernardo Albuquerque 
Carvalho, Maria
Paixão, José António de Carvalho 
Eusébio, M. Ermelinda 
Lopes, Susana Margarida Martins 
Melo, Teresa Margarida Vasconcelos Dias de Pinho e 
Fausto, Rui 
Keywords: 5-acetyl-2-((2-nitrophenyl)amino)thiophene-3-carbonitrile; ROY; color polymorphism; molecular structure; thermal analysis; infrared, Raman and NMR spectroscopies
Issue Date: 10-Jan-2022
Publisher: The Royal Society of Chemistry
Project: UIDB/00313/2020 
Serial title, monograph or event: CrystEngComm
Volume: 24
Issue: 24
Abstract: A novel derivative of the prominent ROY compound, 5-acetyl-2-((2-nitrophenyl)amino)thiophene-3-carbonitrile (AcROY), was synthesized in a two-steps procedure by the nucleophilic aromatic substitution reaction between 1-fluoro-2-nitrobenzene and 2-aminothiophene-3-carbonitrile, followed by Friedel–Crafts acylation at position 5 of the thiophene ring. The conformational space of the compound (isolated molecule) was studied computationally, rendering 4 low-energy intramolecularly hydrogen-bonded conformers. The compound exhibits color polymorphism, with 3 different polymorphs identified. The crystal structures of two of the polymorphs were solved by single-crystal X-ray diffraction crystallography: polymorph 1 (burgundy) is monoclinic (P21/n; a = 5.3354(2) Å, b = 14.2344(4) Å, c = 17.1709(6) Å,  = 96.567(2)º, Z = 4, Z’ = 1), and polymorph 2 (orange) is monoclinic (P21/c; a = 25.451(3) Å, b = 14.4966(14) Å, c = 7.1113(7) Å,  = 95.795(6)º, Z = 8, Z’ = 2. It was not possible to determine the crystal structure of the third polymorph (3, orange-yellowish), but the obtained powder X-ray diffraction, infrared and Raman spectroscopy data clearly demonstrate the existence of this additional polymorphic form. Indexation of its powder diffraction pattern showed that it is a monoclinic variety with lattice parameters a = 11.383(3) Å, b = 13.6609(3) Å, c = 25.247(7) Å, β =101.75(1), thus exhibiting a more complex supramolecular structure compared to polymorphs 1 and 2. All polymorphs were characterized spectroscopically (by infrared and Raman spectroscopies) and by thermal analysis (by differential scanning calorimetry and polarized light thermomicroscopy). Interestingly, among the 4 predicted low energy conformers of the AcROY molecule, only the most stable form was found to be present in the crystals of the two structurally characterized polymorphs of the compound. The dominant intermolecular interactions in polymorphs 1 and 2 were investigated (also using Hirshfeld surface analysis) and were found to be significantly different. The observed polymorphism of AcROY is then an interesting case of packing-determined color polymorphism.
ISSN: 1466-8033
DOI: 10.1039/d1ce01601f
Rights: openAccess
Appears in Collections:I&D CQC - Artigos em Revistas Internacionais

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