Synthesis of Schiff Base Ligand Based on 2-Aminobenzothiazole and 4-Hydroxybenzaldehyde and Their Nickel Complexes: Characterization and Antibacterial Studies

Hana Nurdiana; Sentot Budi Rahardjo; Soerya Dewi Marliyana; Husna Syaima

doi:10.22146/ijc.98008

Synthesis of Schiff Base Ligand Based on 2-Aminobenzothiazole and 4-Hydroxybenzaldehyde and Their Nickel Complexes: Characterization and Antibacterial Studies

https://doi.org/10.22146/ijc.98008

Hana Nurdiana⁽¹⁾, Sentot Budi Rahardjo^(2*), Soerya Dewi Marliyana⁽³⁾, Husna Syaima⁽⁴⁾

(1) Postgraduate Program, Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Sebelas Maret, Jl. Ir. Sutami 36A, Kentingan, Surakarta 57126, Indonesia
(2) Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Sebelas Maret, Jl. Ir. Sutami 36A, Kentingan, Surakarta 57126, Indonesia
(3) Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Sebelas Maret, Jl. Ir. Sutami 36A, Kentingan, Surakarta 57126, Indonesia
(4) Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Mulawarman, Jl. Barong Tongkok No. 4, Gunung Kelua, Samarinda, 75123 Indonesia
(*) Corresponding Author

Abstract

A Schiff base, (E)-4-((benzo[d]thiazol-2-ylimino)methyl)phenol (L¹), was synthesized via the condensation of 2-aminobenzothiazole (L²) with 4-hydroxybenzaldehyde (L³), along with three nickel complexes: [Ni(L¹)₂Cl₂]·5H₂O, [Ni(L²)₆]Cl₂·3H₂O, and [Ni(L³)₆]Cl₂·4H₂O. The compounds were characterized using NMR, AAS, TGA, FTIR, UV-vis, PXRD, molar conductivity, and magnetic susceptibility analyses. Results showed that L¹ acts as a bidentate ligand through its imine and thiazole groups, whereas L² and L³ coordinate via amino and carbonyl groups, respectively. FTIR spectra confirmed Ni–N and Ni–O coordination, while magnetic and electronic spectra indicated octahedral geometries with paramagnetic properties (μ_eff = 2.89–2.98 B.M.). PXRD revealed nanocrystalline phases with high crystallinity (96–99%) and particle sizes of ~44 nm. Conductivity measurements classified the Schiff base nickel complex as a non-electrolyte, whereas the other two were electrolytes. Antibacterial assays demonstrated that [Ni(L¹)₂Cl₂]·5H₂O exhibited significantly higher inhibitory activity against Escherichia coli and Pseudomonas aeruginosa compared to Ni²⁺, the free ligands, and the other nickel complexes. These findings highlight Schiff base nickel complexes, particularly [Ni(L¹)₂Cl₂]·5H₂O, as promising candidates for the development of new antibacterial agents, offering potential alternatives for combating antibiotic-resistant bacterial infections.

Keywords

2-aminobenzothiazole; 4-hydroxybenzaldehyde; Schiff base; nickel complexes; antibacterial activity

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DOI: https://doi.org/10.22146/ijc.98008