Synthesis, X-ray Structure, Cytotoxic, and Anti-Microbial Activities of Zn(II) Complexes with a Hydrazono s-Triazine Bearing Pyridyl Arm

Abstract

The [ZnL(ONO2)2] 1 and [ZnL(NCS)2] 2 complexes were synthesized using self-assembly of the s-triazine tridentate ligand (L) with Zn(NO3)2·6H2O and Zn(ClO4)2·6H2O/NH4SCN, respectively. The Zn(II) is further coordinated by two nitrate and two isothiocyanate groups as monodentate ligands in 1 and 2, respectively. Both complexes have distorted square pyramidal coordination environments where the extent of distortion is found to be greater in 2 (τ5 = 0.41) than in 1 (τ5 = 0.28). Hirshfeld calculations explored the significant C···O, C···C, N···H, and O···H contacts in the molecular packing of both complexes. The energy framework analysis gave the total interaction energies of −317.8 and −353.5 kJ/mol for a single molecule in a 3.8 Å cluster of 1 and 2, respectively. The total energy diagrams exhibited a strong resemblance to the dispersion energy frameworks in both complexes. NBO charge analysis predicted the charges of the Zn(II) in complexes 1 and 2 to be 1.217 and 1.145 e, respectively. The electronic configuration of Zn1 is predicted to be [core] 4S0.32 3d9.98 4p0.45 4d0.02 5p0.01 for 1 and [core] 4S0.34 3d9.97 4p0.53 4d0.02 for 2. The increased occupancy of the valence orbitals is attributed to the donor→acceptor interactions from the ligand groups to Zn(II). The Zn(II) complexes were examined for their cytotoxic and antimicrobial activities. Both 1 and 2 have good cytotoxic efficiency towards HCT-116 and A-549 cancerous cell lines. We found that 1 is more active (IC50 = 29.53 ± 1.24 and 35.55 ± 1.69 µg/mL) than 2 (IC50 = 41.25 ± 2.91 and 55.05 ± 2.87 µg/mL) against both cell lines. Also, the selectivity indices for the Zn(II) complexes are higher than one, indicating their suitability for use as anticancer agents. In addition, both complexes have broad-spectrum antimicrobial activity (IC50 = 78–625 μg/mL) where the best result is found for 2 against P. vulgaris (IC50 = 78 μg/mL). Its antibacterial activity is found to be good compared to gentamycin (5 μg/mL) as a positive control against this microbe.