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1. N-(3-Chloro-4-hydroxyphenyl)acetamide

   https://doi.org/10.1107/S2414314625006959  

   Uppu, Rao M; Fronczek, Frank R (August 2025, IUCrData)

   In the title compound, C₈H₈ClNO₂, the acetamide substituent is twisted out of the phenyl plane, forming a dihedral angle of 58.61 (7)°. In the extended structure, each molecule donates two hydrogen bonds [N—H...O(carbonyl) and O—H...O(carbonyl)] and thus also accepts two such hydrogen bonds. The chlorine atom is not involved in the hydrogen bonding. 

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2. N -(3,5-Dichloro-4-hydroxyphenyl)acetamide

   https://doi.org/10.1107/S2414314626000751  

   Uppu, Rao M; Fronczek, Frank R (January 2026, IUCrData)

   The title compound, C₈H₇Cl₂NO₂, crystallizes in the triclinic space groupP1with three molecules in the asymmetric unit. Two of them are essentially planar, with mean deviations of 13 non-hydrogen atoms of 0.029 and 0.030 Å, and differ only in the conformation of the O—H hydrogen atom. The third molecule is quite nonplanar, with the CCNO acetamide plane forming a dihedral angle of 67.56 (5)° with the remainder of the molecule. In the extended structure, the two almost planar molecules form antiparallel hydrogen-bonded chains through N—H...O interactions of the acetamide substituents. The N—H group of the nonplanar molecule donates a bifurcated hydrogen bond to the O—H group and a Cl substituent of one of the planar molecules. The O—H groups of all molecules form intermolecular hydrogen bonds to other O—H groups or carbonyl O atoms. Together, the hydrogen bonds generate a three-dimensional network. 

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3. N,N0-[Oxybis(benzene-4,1-diyl)]diacetamide

   https://doi.org/10.1107/S2414314625003840  

   Uppu, Rao M; Agu, Ogad A; Babu, Sainath; Mensah, Patrick F; Fronczek, Frank R (May 2025, IUCrData)

   In the title compound, C16H16N2O3, the phenyl groups are twisted away from coplanarity with the ether linkage, forming a dihedral angle of 59.49 (4) with each other. The ether oxygen atom lies somewhat out of both phenyl planes, by 0.066 (2) and 0.097 (2) A ˚ . The acetamide substituents have quite different conformations with respect to the phenyl groups on either side of the molecule. On one side, the C—C—N—C torsion angle is 21.0 (2), while on the other side it is 76.4 (2). In the crystal, the acetamide N—H groups form intermolecular N—H O hydrogen bonds to acetamide O atom, with both NH groups donating to the same molecule. Thus, ladder-like chains exist in the [101] direction. One of the methyl groups has its H atoms disordered into two orientations, and the crystal chosen for data collection was found to be twinned. 

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4. Structural insights into supramolecular interactions in isostructural salts of 2,4,6-triaminopyrimidinium with various heterocyclic carboxylates

   https://doi.org/10.1107/S2053229624008787  

   Mohana, Marimuthu; Gomathi, Sundaramoorthy; Thomas_Muthiah, Packianathan; Butcher, Ray J (November 2024, Acta Crystallographica Section C Structural Chemistry)

   2,4,6-Triaminopyrimidine is an interesting and challenging molecule due to the presence of multiple hydrogen-bond donors and acceptors. Its noncovalent interactions with a variety of carboxylic acids provide several supramolecular aggregates with frequently occurring molecular synthons. The present work focuses on the supramolecular interactions of 2,4,6-triaminopyrimidinium 3-(indol-3-yl)propionate–3-(indol-3-yl)propionic acid (1/1), C₄H₈N₅⁺·C₁₁H₁₀NO₂⁻·C₁₁H₁₁NO₂, (I), 2,4,6-triaminopyrimidinium 2-(indol-3-yl)acetate, C₄H₈N₅⁺·C₁₀H₈NO₂⁻, (II), 2,4,6-triaminopyrimidinium 5-bromothiophene-2-carboxylate, C₄H₈N₅⁺·C₅H₂BrO₂S⁻, (III), and 2,4,6-triaminopyrimidinium 5-chlorothiophene-2-carboxylate, C₄H₈N₅⁺·C₅H₂ClO₂S⁻, (IV). All four salts exhibit robust homomeric and heteromericR₂²(8) ring motifs. Salts (I) and (II) develop sextuple [in (I)] and quadruple [in (I) and (II)] hydrogen-bonded arrays through fused-ring motifs. Salt (II) exhibits a rosette-like architecture. Salt (IV) is isostructural and isomorphous with salt (III), exhibiting an identical crystal structure with a different composition and an identical supramolecular architecture. In salts (III) and (IV), a linear hetero-tetrameric motif is formed and, in addition, both salts exhibit halogen–π interactions which enhance the crystal stability. All four salts develop a supramolecular hydrogen-bonded pattern facilitated by several N—H...O and N—H...N hydrogen bonds with multiple furcated donors and acceptors. 

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5. N -(4-Methoxy-2-methyl-5-nitrophenyl)acetamide

   https://doi.org/10.1107/S2414314625004705  

   Uppu, Rao M; Fronczek, Frank R (June 2025, IUCrData)

   In the title compound, C10H12N2O4, the four substituents lie out of the phenyl plane by varying degrees. The methyl C atom lies 0.019 (3) A ˚ out of plane, while the methoxy O and C atoms lie 0.067 (2) and 0.042 (3) A ˚ out of plane, respectively, with the C—C—O—C torsion angle being 3.3 (2). The plane of the nitro group is twisted out of the phenyl plane, forming a dihedral angle of 12.03 (9) with it. The acetamide substituent is twisted considerably more out of the phenyl plane, forming a dihedral angle of 47.24 (6) with it. In the extended structure, the acetamide NH group donates a hydrogen bond to an acetamide carbonyl O atom, thereby forming chains propagating in the [010] direction. 

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