Syntheses and Structural Investigations of Penta-Coordinated Co(II) Complexes with -Pyrazolo--Triazine Pincer Ligands, and Evaluation of Their Antimicrobial and Antioxidant Activities.

Two penta-coordinated ; and ; complexes with the -pyrazolyl--triazine pincer ligands and were synthesized and characterized. Both and act as NNN-tridentate pincer chelates coordinating the Co(II) center with one short Co-N(-triazine) and two longer Co-N(pyrazole) bonds. The coordination number of Co(II) is five in both complexes, and the geometry around Co(II) ion is a distorted square pyramidal in while shows more distortion. In both complexes, the packing is dominated by Cl…H, C-H…π, and Cl…C (anion-π stacking) interactions in addition to O…H interactions, which are found only in . The UV-Vis spectral band at 564 nm was assigned to metal-ligand charge transfer transitions based on TD-DFT calculations. Complexes and showed higher antimicrobial activity compared to the respective free ligand and which were not active. MIC values indicated that had better activity against , and than . DPPH free radical scavenging assay revealed that all the studied compounds showed weak to moderate antioxidant activity where the nature of the substituent at the -triazine core has a significant impact on the antioxidant activity.