Home Physical Sciences The crystal structure of 6-hydroxy-5H-pyrrolo[3,4-b]pyridine-5,7(6H)-dione monohydrate, C7H6N2O4
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The crystal structure of 6-hydroxy-5H-pyrrolo[3,4-b]pyridine-5,7(6H)-dione monohydrate, C7H6N2O4

  • Feng Xu ORCID logo EMAIL logo , Hui Yu and Shilin Zheng
Published/Copyright: September 23, 2025

Abstract

C7H6N2O4, monoclinic, P21/c (no. 14), a = 8.1416(3) Å, b = 10.2220(3) Å, c = 9.2212(3) Å, β = 91.7600(10)°, V = 767.06(4) Å3, Z = 15, R gt (F) = 0.1022, wRref(F2) = 0.1077, T = 296.15 K.

CCDC no.: 2469492

The molecular structure is shown in the figure. Table 1 contains the crystallographic data and the list of the atoms including atomic coordinates and displacement parameters can be found in the cif-file attached to this article.

Table 1:

Data collection and handling.

Crystal: Colourless block
Size: 0.20 × 0.15 × 0.10 mm
Wavelength: Mo Kα radiation (0.71073 Å)
μ: 0.13 mm−1
Diffractometer, scan mode: Bruker Apex2, φ and ω scan
θmax, completeness: 27.6°, 100 %
N(hkl)measured, N(hkl)unique, Rint: 12460, 1,776, 0.020
Criterion for Iobs, N(hkl)gt: Iobs > 2 σ(Iobs), 1573
N(param)refined: 130
Programs: Olex2, 1 SHELX, 2 , 3 Bruker 4

1 Source of materials

All chemicals were purchased from commercial sources and used as received without further purification, and 2,3-pyridinedicarboxylic anhydride was synthesized by our laboratory. Under N2, anhydrous sodium acetate (3.956 g, 48.2 mmol) and hydroxylamine hydrochloride (3.956 g, 57.1 mmol) were dissolved in acetic acid (25 mL). Then, the above mixture solution was refluxed for 5 min. The mixture was filtered to remove precipitated NaCl. And then, 2,3-pyridinedicarboxylic anhydride (3.956 g, 26.6 mmol) was added to the filtrate, and the mixture was refluxed for 25 min. After completion, the mixture was filtered and concentrated to a saturated solution under vacuum, a yellow precipitate is formed. The precipitate was collected by filtration, washed with diethyl ether. The crystals were obtained by recrystallization in the cooled acetonitrile solution. 1H NMR (400 MHz, DMSO‑d6) δ: 11.04 (s, 1H) 8.94 (m, 1H), 8.24 (m, 1H), 7.77 (m, 1H). 13C NMR (101 MHz, DMSO‑d6) δ: 162.66, 154.58, 149.01, 130.96, 128.03, 125.32.

2 Experimental details

Olex2 1 software and the SHELXL 2 refinement were used to solve and refine the crystal structure. Hydrogen atoms were placed in their geometrically idealized positions and constrained to ride on their parent atoms.

3 Comment

Organic nitrogen hydroxy compounds (N–OH), as a novel class of organic catalysts, with N-hydroxyphthalimide (NHPI) being the most representative, have recently been employed as an effective system for C–H bonds activation via hydrogen extraction. 5 , 6 , 7 , 8 , 9 The molecule features the unique properties of the N–OH function which is different from the previously proposed systems. 10 , 11 Thus, organic nitrogen hydroxy compounds have attracted increasing interest from both the academic and industrial communities over the past decade. 12 These compounds primarily achieve classical C–H bond oxidation reactions through the homolytic cleavage of the hydroxyl bond in N–OH to form N-oxyl radical. 13 , 14 , 15 As a result, this kind of compound has a wide range of applications in carbon-carbon, carbon-nitrogen, and carbon-silicon bond formation reactions. 12 With the continuous in-depth research on the synthesis and application of organic nitrogen hydroxy compounds, exploring the structural characteristics of these compounds is of great significance for understanding their structure-activity relationships.

However, reports on the crystal structures of organic nitrogen hydroxy compounds remain limited. To date, only two classes of symmetrical organic nitrogen hydroxyl compounds have been reported, i.e., HPPDO 16 and DNHPI. 17

The molecular structure comprises at least two distinct planes: the pyridine ring plane, the pyrrole ring plane. In the crystal, the torsion angles of the nitrogen hydroxyl group (angle N(1)–O(4)H) is 106.8°. The O–H bond length in the nitrogen hydroxyl group is 0.95 Å, which is longer than the O–H bond length in water molecules (0.85 Å). Additionally, the hydrogen in the nitrogen hydroxyl group can form hydrogen bonds with water molecules, which are present. All geometric parameters fall within expected ranges. 16 , 17


Corresponding author: Feng Xu, School of Materials Science, Guiyang University, Guiyang 550005, Guizhou Province, P.R. China, E-mail:

Hui Yu and Feng Xu contributed to the work equally and should be regarded as co-first authors.


Funding source: Guiyang University Multidisciplinary Team Construction Projects in 2025

Award Identifier / Grant number: Gyxk202505

Funding source: Research Fund of Guizhou Provincial Department of Education

Award Identifier / Grant number: Qianjiaoji[2024]284

  1. Research funding: We gratefully acknowledge support by the Guiyang University Multidisciplinary Team Construction Projects in 2025 [Gyxk202505] and Research Fund of Guizhou Provincial Department of Education (No. Qianjiaoji[2024]284).

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Received: 2025-07-09
Accepted: 2025-09-02
Published Online: 2025-09-23
Published in Print: 2025-12-17

© 2025 the author(s), published by De Gruyter, Berlin/Boston

This work is licensed under the Creative Commons Attribution 4.0 International License.

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