Synthesis, characterization, photoluminescence properties, DFT studies, photocatalytic and antifungal activity of a new pyrazole-containing thiosemicarbazone ligand and its Co(III) and Ni(II) complexes

A new pyrazole-based thiosemicarbazone ligand, 5-methyl-3-formylpyrazole-N(4)-dipentylthiosemicarbazone (HMP(z)NPent(2)) (1), and its Co(III) and Ni(II) complexes, [Co(MP(z)NPent(2))(2)]Br (2) and [Ni(HMP(z)NPent(2))(2)]Cl-2 (3), respectively, were synthesized and characterized. Complexes 2 and 3 are cationic in nature and behave as 1:1 and 1:2 electrolytes in MeOH, respectively. Electronic spectral features of the complexes indicate distorted octahedral structures. IR spectral data (4000-450 cm(-1)) suggest monoprotic tridentate (NNS) coordination of 1 to Co(III) via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulfur; In contrast, 1 is a neutral NNS tridentate donor in 3, coordinating to Ni(II) via the pyrazolyl iminic nitrogen, azomethine nitrogen and thioketo sulfur. Structural features of the compounds were confirmed by DFT calculations. TD-DFT absorption spectra authenticate that the simulated peaks are in reasonable agreement with the experimentally resolved peaks. Fluorescence spectral studies revealed photoluminescent behavior. The three compounds reported here have photocatalytic activity. 1 (used as positive control) and 3 show similar antifungal activity in inhibiting the growth of the phytopathogen Colletotrichum siamense (CS), whereas 2 is less efficient to control the growth of CS. Both 3 and 2 show antifungal activity against Colletotrichum gloeosporioides (AP2). Compound 3 is more effective to prevent the growth of phytopathogen Fusarium equisetum (F.E) than 2 and 1 (positive control).