The crystal structure of diammonium 2,5-dihydroxyterephthalate, C8H12N2O6

Zhenxiu Si; Yanyu Lv; Yingying Xu; Lingyun Jiang

doi:10.1515/ncrs-2025-0275

Article Open Access

The crystal structure of diammonium 2,5-dihydroxyterephthalate, C₈H₁₂N₂O₆

Zhenxiu Si , Yanyu Lv , Yingying Xu and Lingyun Jiang

Published/Copyright: September 17, 2025

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From the journal Zeitschrift für Kristallographie - New Crystal Structures

Abstract

C₈H₁₂N₂O₆, monoclinic, P2₁/n (no. 14), a = 3.8391(8) Å, b = 8.8332(18) Å, c = 14.487(3) Å, β = 95.62(3)°, V = 488.92(18) Å³, Z = 2, R_gt(F) = 0.0327, wR_ref(F²) = 0.0949, T = 293 K.

CCDC no.: 2450201

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:	Brown block
Size:	0.41 × 0.31 × 0.23 mm
Wavelength:	Mo Kα radiation (0.71073 Å)
μ:	0.14 mm⁻¹
Diffractometer, scan mode:	Rigaku R-AXIobsS RAPIobsD, ω scans
θ_max, completeness:	24.9°, 99 %
N(hkl)_measured, N(hkl)_unique, R_int:	3649, 840, 0.041
Criterion for I_obs, N(hkl)_gt:	I_obs > 2 σ(I_obs), 737
N(param)_refined:	90
Programs:	Rigaku ¹ , SHELX ² ^, ³

1 Source of materials

2,5-Dihydroxyterephthalic acid (99 mg, 0.5 mmol) was dissolved in a mixed solvent of ethyl alcohol-water (v:v = 1:1), followed by the addition of aqueous ammonia (2 mL, 25–28 %). After vigorous stirring, the solution was filtered and allowed to stand undisturbed at room temperature. Brown block-shaped crystals were obtained after 3 days by slow evaporation.

2 Experimental details

The structure was solved by Direct Methods with the SHELXS program. All H-atoms from C atoms were positioned with idealized geometry and refined isotropically (U_iso(H) = 1.2U_eq(C) for aromatic and methylene H atoms, respectively), using a riding model with C–H = 0.93 Å or 0.96 Å. H atoms attached to O atoms were found in a difference Fourier synthesis and were refined using a riding model, with the O–H distances fixed as initially found and with U_iso(H) values set at 1.5U_eq(O).

3 Comment

Noncovalent interactions, including ionic bonds, hydrogen bonds, and van der Waals forces, play important roles in molecular recognition, crystal engineering, and supramolecular assembly. ⁴ ^, ⁵ ^, ⁶ ^, ⁷ ^, ⁸ Among these, ammonium carboxylate systems ( NH 4 + ⋯RCOO⁻) serve as ideal models for investigating the interplay of electrostatic attraction and hydrogen bonding, as they exhibit robust and tunable interactions. ⁹ ^, ¹⁰ ^, ¹¹ ^, ¹² The ammonium ion ( NH 4 + ) can form multiple hydrogen bonds with carboxylate groups (RCOO⁻), while the aromatic backbone introduces additional π⋯π stacking and van der Waals contributions. Understanding such cooperative interactions is crucial for designing functional materials and elucidating biological processes, such as enzyme-substrate binding or ion transport. ¹³ ^, ¹⁴ ^, ¹⁵ ^, ¹⁶ Recent studies have explored ammonium carboxylate salts to decipher the balance between ionic and hydrogen-bonding forces in crystalline frameworks. ¹⁷ For instance, systems like ammonium terephthalate or formate have demonstrated how NH 4 + ⋯RCOO⁻ motifs direct lattice packing. ¹⁸ ^, ¹⁹ ^, ²⁰ However, most studies focus on simple carboxylates, neglecting the role of auxiliary functional groups (e.g., hydroxyls) that could enhance hydrogen-bond networks or introduce steric effects. ²¹

Single-crystal X-ray diffraction analysis revealed that title compound crystallizes in the monoclinic system with the space group P2₁/n The asymmetric unit of title compound consists of one ammonium cation and half of a 2,5-dihydroxyterephthalate anion. The N–H bond lengths in the NH 4 + ion range from 0.889(2) to 0.911(2) Å, with bond angles between 106.97(2)° and 114.3(2)°, indicating a slightly distorted tetrahedral configuration. The carboxylate group of the 2,5-dihydroxyterephthalate forms a dihedral angle of 1.2(1)° with the benzene ring plane, demonstrating good coplanarity. Intramolecular hydrogen bonding is observed within the carboxylate group (d(O3⋯O2ⁱ) = 2.515 Å and O–H⋯O = 147°; symmetry code: i = −x + 2, –y + 1, −z + 1). The hydroxyl groups form intermolecular hydrogen bonds with adjacent 2,5-dihydroxyterephthalate ions, generating an infinite one-dimensional chain extending along the [010] direction. ²² These chains further assemble into a two-dimensional layered structure parallel to the (001) plane via π⋯π stacking interactions between benzene rings, the mean interplanar distance between the neighboring benzene rings is 3.48(2) Å. Finally, the layers are interconnected through intermolecular hydrogen bonds between the hydrogen atoms of NH 4 + and the carboxylate/hydroxyl oxygen atoms of 2,5-dihydroxyterephthalate, completing a three-dimensional supramolecular framework (d(N⋯O) = 2.804–3.042 Å and N–H⋯O = 149°–171°). ²³ ^, ²⁴

Corresponding author: Zhenxiu Si, Department of Pharmaceutical Engineering, Shandong Drug and Food Vocational College, Weihai 262400, People’s Republic of China, E-mail: 231212@sddfvc.edu.cn

Acknowledgments

This work was supported by the Ningbo Natural Science Foundation (no. 2019A610150).

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Received: 2025-06-16

Accepted: 2025-07-21

Published Online: 2025-09-17

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