Novel Cu II and Cr III Triazole–Pyrazole Complexes: Synthesis, Structural Characterization, and Antibacterial Evaluation

Abstract

A bidentate ligand 1‐methyl‐3‐(5‐methyl‐1H‐pyrazol‐3‐yl)‐1H‐1,2,4‐triazole ( L21 ), and transition‐metal complexes, [Cu(L21) 2 (NO 3 ) 2 ] ( 1 ) and [Cr 2 (L21) 4 (OH) 2 ](NO 3 ) 4 ( 2 ), were synthesized and characterized by single‐crystal X‐ray diffraction, FT‐IR, UV–vis spectroscopy, and high‐resolution mass spectrometry. Complex 1 contains a Cu II center located on an inversion center with chelating L21 ligands in the equatorial plane and coordinated nitrate anions, while 2 is a dinuclear Cr III complex with a Cr···Cr separation of 2.998 Å, stabilized by bridging hydroxide ligands and counterbalanced by lattice nitrate anions. While L21 showed negligible antibacterial activity, its coordination with metal centers led to a marked improvement. In assays against E. coli , P. aeruginosa , S. aureus , and B. subtilis , 2 exhibited inhibition zones ranging from 9.75 ± 0.92 to 10.25 ± 0.31 mm and a minimum inhibitory concentration of 2.5 mmol/L. Frontier orbital analysis revealed a higher electrophilicity index for 2 ( ω  = 50.19/48.95 eV) compared with 1 ( ω  =  2.92/7.26 eV), indicating a greater tendency to accept electron density, while Hirshfeld and noncovalent interaction analyses revealed a denser interaction network in 2 . Molecular docking against aquaporins, S. aureus phosphofructokinase, and human serum albumin revealed stronger predicted binding affinities for 2 . L21 is a tunable scaffold for developing biologically active transition‐metal complexes with antibacterial properties.