A new approach to study semi-coordination using two 2-methyl-5-nitroimidazole copper() complexes of biological interest as a model system

• Published in: RSC advances 2023-09, Vol.13 (4), p.27997-287
• Main Authors: Fachini, Lucas G, Baptistella, Gabriel B, Postal, Kahoana, Santana, Francielli S, de Souza, Emanuel M, Ribeiro, Ronny R, Nunes, Giovana G, Sá, Eduardo L
• Format: Article
• Language: English
• Subjects: Bonding strength; Chemistry; Coordination; Copper; Density functional theory; E coli; Elongation; Single crystals; X ray powder diffraction
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d3ra02130k

Two novel copper( ii ) complexes [Cu(2mni) 2 (H 2 O) 2 ](NO 3 ) 2 ·2H 2 O ( 1 ) and [Cu(2mni) 2 (NO 3 ) 2 ] ( 2 ), where 2mni is 2-methyl-5-nitroimidazole, were prepared and characterized in the solid state using single-crystal and powder X-ray diffraction analyses, EPR, electronic and vibrational spectroscopies (FTIR and Raman), and thermogravimetric methods. Both products present an elongated distorted octahedral geometry with axial Cu-O bond lengths of 2.606(14) and 2.593(15) Å, indicating semi-coordination. Density functional theory (DFT) calculations at the B3LYP/LANL2DZ theory level were used to study the electronic properties of 1 and 2 . The Independent Gradient Model (IGM) was employed to determine the Intrinsic Bond Strength Index (IBSI) of the semi-coordination and to plot δ g isosurfaces for the electronic sharing between the metal center and ligands. A moderate to weak antibacterial activity against Escherichia coli cultures was found for 1 with a 50% growth inhibition (GI 50 ) value of 0.25 mmol L −1 . To the best of our knowledge, this is the first time that the semi-coordination analysis using IGM was carried out for a copper( ii ) complex with axial elongation, finding a good correlation between the bond length and the IBSI, and the study was extended for a series of analogous complexes described in the literature. Two copper( ii ) complexes with 2-methyl-5-nitroimidazole ligand were prepared and characterized by spectroscopic and diffractometric techniques. The weak semicoordination was studied by DFT and IGM. Antibacterial assays were also conducted.