Synthesis and Structural Characterization of Two New Charge-Assisted Hydrogen-Bonded Supramolecular Networks in 2-Amino-4-methylpyridinium Isophthalate Dihydrate and 2-Amino-5-methylpyridinium Hydrogen Isophthalate

Abstract

Two new supramolecular compounds, 2C₆H₉N₂⁺. C₈H₄O₄⁻.2H₂O /(4AMPIP) (1) and C₆H₉N₂⁺.C₈H₅O₄⁻/(5AMPHIP) (2), were synthesized and characterized by IR spectra, ¹HNMR, ¹³CNMR, and single-crystal X-ray diffraction. Compound 1 crystallizes in the monoclinic system, space group Cc, with a = 7.8914(3), b = 38.4226(16), c = 7.3354(3) Å, β = 107.9460(10)˚, V = 2115.94(15) ų, D_c = 1.314 g/cm³, F(000) = 888, μ = 0.10 mm⁻¹, Z = 4, the final R = 0.0298, and wR = 0.0835 for 3135 observed reflections with I > 2σ(I); and compound 2 crystallizes in the monoclinic system, space group P2₁/c, with a = 9.0126(2), b = 12.2055(3), c = 12.3170(2) Å, β = 104.2160(10)°, V = 1313.42(5) ų, D_c = 1.387 g/cm³, F(000) = 576, μ = 0.103 mm⁻¹, Z = 4, the final R = 0.0454, and wR = 0.1130 for 2799 observed reflections with I > 2σ(I). The 2-amino-4-methylpyridinium (4AMP) and 2-amino-5-methylpyridinium (5AMP) cations are protonated at one of the pyridinium N atoms. In both compounds, the isophthalate anion interacts with protonated cations through a pair of N‒HċċċO hydrogen bonds to form a cyclic hydrogen-bonded motif with graph-set notation (R₂²(8)). In the crystal structure of 1, the ion pairs (whether cation/anion) are linked by water molecules through O‒HċċċO, N‒HċċċO, and weak C‒HċċċO hydrogen bonds, forming a three-dimensional network. In the crystal structure of 2, there are chains and layer made up of the O‒HċċċO, N‒HċċċO, and C‒HċċċO hydrogen bonds, forming a two-dimensional network.

Keywords:

• Aminopyridine
• crystal structure
• FTIR and NMR spectra
• hydrogen- bond network
• isophthalic acid
• proton-transfer
• supramolecular heterosynthon

Acknowledgments

The authors thank the Malaysian Government and Universiti Sains Malaysia (USM) for the research facilities and USM Short Term Grant, No. 304/PFIZIK/6312078 to conduct this work. KT thanks the Academy of Sciences for the Developing World and USM for the TWAS–USM fellowship.