| Summary: | Condensation of the reaction between enrofloxacin and ethylenediamine in the existence of glacial acetic acid produced a new N,N-ethylene (bis 1-cyclopropyl-7-(4-ethylpiperazin-1-yl)-6-fluoro-1,4-dihydroquinoline-3-carboxylic acid Schiff base (<b>H<sub>2</sub>Erx-en</b>). <b>H<sub>2</sub>Erx-en</b> was used as a tetra-dentate ligand to produce novel complexes by interacting with metal ions iron(III), yttrium(III), zirconium(IV), and lanthanum(III). The synthetic <b>H<sub>2</sub>Erx-en</b> and its chelates had been detected with elemental analysis, spectroscopic methods, mass spectrometry, thermal studies, conductometric and magnetic measurements experiments. The calculated molar conductance of the complexes in 1 × 10<sup>−3</sup> M DMF solution shows that iron(III), yttrium(III) and lanthanum(III) are 1:1 electrolytes, however the zirconium(IV) complex is non-electrolyte. The infrared spectra of <b>H<sub>2</sub>Erx-en</b> chelates indicated that the carboxylic group is deprotonated and <b>H<sub>2</sub>Erx-en</b> is associated with metals as a tetra-dentate through nitrogen and oxygen atoms. The disappearance of the carboxylic proton in all complexes corroborated information concerning <b>H<sub>2</sub>Erx-en</b> deprotonation and complexation with metal ions, according to <sup>1</sup>H NMR data. Thermal analysis revealed the abundance of H<sub>2</sub>O particles in the chelates’ entrance and outlet spheres, indicating the disintegration pattern of <b>H<sub>2</sub>Erx-en</b> and their chelates. The Coats–Redfern and Horowitz–Metzeger approaches were utilized to calculate the thermodynamic items (E<sub>a</sub>, ΔS *, ΔH *, and ΔG *) at n = 1 and n ≠ 1. The resulting data reveal better organized chelate building activation. Density functional theory (DFT) was created to properly grasp the optimal architecture of the molecules. The chelates are softer than <b>H<sub>2</sub>Erx-en</b>, with estimates varying between 95.23 eV to 400.00 eV, compared to 31.47 eV for <b>H<sub>2</sub>Erx-en</b>. The disc diffusion technique was utilized to assess <b>H<sub>2</sub>Erx-en</b> and their chelates in an antimicrobial assay against various food and phytopathogens. The zirconium(IV) chelate has the most potent antibacterial action and is particularly efficient against <i>Salmonella typhi</i>.
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