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<p>Two positional isomers of nitro-hydroxy nicotinic acid, 1<i>H</i>-3-carboxy-5-nitropyridin-2-one (3c5n) and 1<i>H</i>-5-carboxy-3-nitropyridin-2-one (5c3n), both adopt the amide tautomer in the solid state and crystallize in noncentrosymmetric space groups (3c5n: two polymorphs, crystallizing together, <i>P</i>2<sub>1</sub>2<sub>1</sub>2<sub>1</sub> and <i>P</i>2<sub>1</sub>2<sub>1</sub>2; 5c3n: <i>Pna</i>2<sub>1</sub>). Polymorph 3c5n-II is ~ 0.15&#xa0;g cm<sup>− 3</sup> less dense than 3c5n-I owing to isolated voids (~ 18 Å<sup>3</sup> each), yet single-crystal X-ray diffraction, DSC/TGA analyses, and micro-FTIR rule out solvent inclusion, establishing 3c5n-II as a solvent-free polymorph with reduced packing efficiency. In both polymorphs, identical O–H···O chains generated by 2<sub>1</sub> axis define the primary supramolecular synthon. However, the secondary assembly of these chains differs: the undulating chains of 3c5n-I pack closely to form a dense structure, whereas the nearly planar chains of 3c5n-II assemble less efficiently and thereby generate the voids. NO₂···π(pyridin-2-one) contacts form ladder motifs along the shortest unit cell axis; together with the 2<sub>1</sub> chains, these motifs favor noncentrosymmetric packing. Periodic DFT (PBE0-D3/def2-TZVPP) gives nearly identical lattice/cohesive energies for 3c5n-I and 3c5n-II despite the density contrast. Relative to 3c5n, the 5c3n isomer gains an additional intermolecular O–H···O bond and a slightly more favorable lattice and cohesive energy, but the total crystal energies remain comparable, suggesting compensation between inter- and intramolecular hydrogen bonding.</p>

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Non-centrosymmetric polymorphs and isomers of hydroxy-nitro derivatives of nicotinic acid: Contrasting densities and convergent packing motifs

  • 期刊论文

  • 发表日期：

    2025年12月9日

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  • Ivan V. Fedyanin,
  • Rinat R. Aysin,
  • Valentina A. Karnoukhova

摘要

Two positional isomers of nitro-hydroxy nicotinic acid, 1H-3-carboxy-5-nitropyridin-2-one (3c5n) and 1H-5-carboxy-3-nitropyridin-2-one (5c3n), both adopt the amide tautomer in the solid state and crystallize in noncentrosymmetric space groups (3c5n: two polymorphs, crystallizing together, P212121 and P21212; 5c3n: Pna21). Polymorph 3c5n-II is ~ 0.15 g cm− 3 less dense than 3c5n-I owing to isolated voids (~ 18 Å3 each), yet single-crystal X-ray diffraction, DSC/TGA analyses, and micro-FTIR rule out solvent inclusion, establishing 3c5n-II as a solvent-free polymorph with reduced packing efficiency. In both polymorphs, identical O–H···O chains generated by 21 axis define the primary supramolecular synthon. However, the secondary assembly of these chains differs: the undulating chains of 3c5n-I pack closely to form a dense structure, whereas the nearly planar chains of 3c5n-II assemble less efficiently and thereby generate the voids. NO₂···π(pyridin-2-one) contacts form ladder motifs along the shortest unit cell axis; together with the 21 chains, these motifs favor noncentrosymmetric packing. Periodic DFT (PBE0-D3/def2-TZVPP) gives nearly identical lattice/cohesive energies for 3c5n-I and 3c5n-II despite the density contrast. Relative to 3c5n, the 5c3n isomer gains an additional intermolecular O–H···O bond and a slightly more favorable lattice and cohesive energy, but the total crystal energies remain comparable, suggesting compensation between inter- and intramolecular hydrogen bonding.