Two new Zn(II) complexes with tridentate hydrazone-based ligands (condensation products of 2-acetylthiazole) were synthesized and characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy and single crystal X-ray diffraction methods. The complexes 1, 2 and recently synthesized [ZnL³(NCS)₂] (L³ = (E)-N,N,N-trimethyl-2-oxo-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)ethan-1-aminium) complex 3 were tested as potential catalysts for the ketone-amine-alkyne (KA²) coupling reaction. The gas-phase geometry optimization of newly synthesized and characterized Zn(II) complexes has been computed at the density functional theory (DFT)/B3LYP/6–31G level of theory, while the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO and LUMO) energies were calculated within the time-dependent density functional theory (TD-DFT) at B3LYP/6-31G and B3LYP/6-311G(d,p) levels of theory. From the energies of frontier molecular orbitals (HOMO–LUMO), the reactivity descriptors, such as chemical potential (μ), hardness (η), softness (S), electronegativity (χ) and electrophilicity index (ω) have been calculated. The energetic behavior of the investigated compounds (1 and 2) has been examined in gas phase and solvent media using the polarizable continuum model. For comparison reasons, the same calculations have been performed for recently synthesized [ZnL³(NCS)₂] complex 3. DFT results show that compound 1 has the smaller frontier orbital gap so, it is more polarizable and is associated with a higher chemical reactivity, low kinetic stability and is termed as soft molecule.

In this study, a tetradentate 1,3‐propanediamine‐ N,N′- diacetate (1,3‐pdda ²⁻ ) was utilized for the synthesis of a dinuclear gallium(III) complex, uns‐ cis ‐[Ga(1,3‐pdda)( µ ‐OH)] ₂ ^. 2H ₂ O ( 1 ). Complex 1 was characterized using IR and NMR ( ¹ H and ¹³ C) spectroscopy, and its crystal structure was determined by single‐crystal X‐ray diffraction analysis. Both Ga(III) ions in Complex 1 exhibit octahedral geometry, with each ion coordinated by two nitrogen and two oxygen atoms from the 1,3‐pdda ^2– ligand, as well as two oxygen atoms from the bridging hydroxyl groups. IR and NMR ( ¹ H and ¹³ C) spectra were simulated using DFT methods, showing a high degree of correlation with experimental data. Hirshfeld surface analysis provided insights into intermolecular interactions, with H⋯O and H⋯H interactions contributing significantly to the crystal stability. The antimicrobial potential of Complex 1 was evaluated alongside previously synthesized gallium(III) complexes, Na[Ga(1,3‐pdta)]·3H ₂ O ( 2 ) and Ba[Ga(1,3‐pndta)] ₂ ·3H ₂ O ( 3 ), with 1,3‐pdta ⁴⁻ (1,3‐propanediamine‐ N,N,N′,N′ ‐tetraacetate) and 1,3‐pndta ⁴⁻ ((±)‐1,3‐pentanediamine‐ N,N,N′,N′ ‐tetraacetate), respectively. Among all the tested microbial species, the gallium(III) complexes have shown selective activity against Pseudomonas aeruginosa PAO1 strain and were able to reduce pyocyanin production by 40–43% in the clinical isolate BK25H of this bacterium. Moreover, Complexes 1 – 3 can modulate the quinolone‐mediated quorum sensing system in P. aeruginosa PAO1. Interaction studies with calf thymus DNA (ct‐DNA) and bovine serum albumin (BSA) were conducted to evaluate the binding affinity and mode of interaction of Complex 1 with key biomolecules, aiming to assess its potential for transport via serum proteins and its safety profile in terms of DNA interactions. Spectrofluorimetric experiments and molecular docking revealed that Complex 1 binds strongly to the Site I on BSA, with weaker interactions at the Site II. While spectrofluorimetric studies showed that Complex 1 has a slight affinity for minor groove binding or intercalation to ct‐DNA, docking studies suggested some minor groove binding, especially in larger DNA sequences, with enhanced stabilization in 10‐bp‐DNA through hydrogen and carbon bonds.