A cationic Co(II) coordination polymer 1[Co(-L)(-Cl)(H2O)2]+ with the 4-amino-4H-1,2,4-triazole ligand: Structure, thermal behavior, and antimicrobial activity

We report a combined experimental and theoretical study on a Co(II) coordination polymer 1 infinity[Co(mu-L)(mu-Cl) (H2O)2]Cl based on 4amino4H-1,2,4-triazole (L). Single crystal X-ray diffraction showed that the Co(II) ions are coordinated by the N1 and N2 atoms of the bridging 4amino-1,2,4-triazole ligand, two trans-oriented bridging Cl ligands and two O atoms from coordinated water molecules in a distorted octahedral geometry. The ligand shows a bridging mu-kappa 1,kappa 1,(N,N) coordination with Cl-Cl-N-N-Co five membered rings in the polymeric strand. Intra and intermolecular N-H...O and O-H...Cl hydrogen bonding interactions stabilize the crystal structure. Hirshfeld surface analysis in combination with ATR-FTIR, and FTRaman spectroscopy were carried out to study the multitude of noncovalent interactions. Geometry optimization using density functional theory (DFT) calculations on the monomolecular model [Co(L)2Cl2(H2O)2] on B3LYP/6-311++G(2d,2p) level gave good agreement with the metrics found in the crystal structure and also agreed quite well with the experimental IR and Raman data, thus allowing spectral assignments. Thermogravimetric (TGA) and Differential Scanning Calorimetric (DSC) experiments coupled with mass spectrometry (MS) under an argon atmosphere in the temperature range 25 to 950 degrees C showed thermal stability till about 100 degrees C. The compound showed inhibitory activity against the Gramnegative bacterium E. fergusonii, the Gram-positive bacteria S. aureus, E. feacalis, and B. cereus, and the yeast C. parapsilosis in agar diffusion experiments at a concentration of 1.25 and 2.50 mg/mL with inhibition zones of 10 to 20 mm in 24 h, but not against the Gramnegative E. coli and the yeast C. sake.