First divalent copper complex of a terdentate thiosemicarbazido-pyrazoline derived from 2,4-pentanedione bis(thiosemicarbazone): Synthesis, structural characterisation and antimicrobial in vitro activity assessment

Abstract Reaction of 2,4-pentanedione with thiosemicarbazide in 1:2 ratio produces cyclic pyrazoline thiosemicarbazone (H2L2 with L2 = C7H12N6S2). The obtained ligand has been characterized by elemental analysis, UV-Visible, FTIR, 1H and 13C NMR. The results suggest that the ligand is in pyrazolinic form, and finally the structure has been confirmed by single crystal X-ray diffraction. The [(L2•)Cu(SCN)] copper complex has been prepared by reaction of H2L2 and thiocyanate salt with copper acetates and has been fully characterized by single crystal X-ray diffraction, Hirshfeld surface analysis, as well as UV-Visible, FTIR, and Raman spectroscopies. TGA analysis and magnetic measurements were also performed. Single-crystal X-ray diffraction reveals that the complex is a neutral monomer with copper in distorted tetrahedral environment. The anionic ligand (L2•)- remained in cyclic form and is coordinated as terdentate ligand (SNS). The title complex results from a double deprotonation coupled with a monoelectronic oxidation of H2L2 and it may be seen as a CuII-ligand radical type complex. The copper ion is tetra coordinated (CuN2S2) by two sulfur and one nitrogen of (L2•)- and by thiocyanate nitrogen atoms. The new [(L2•)Cu(SCN)] complex crystallizes in the monoclinic system and C 2/c space group. Full-Potential Linearized Augmented Planewave Method (FLAPW) calculations based on the Density-Functional Theory (DFT) principle are performed to shed light on both electronic and magnetic structures as well. [(L2•)Cu(SCN)] showed a greater activity than its parental ligand H2L2 against two strains of the phytopathogenic fungus Verticillium dahliae while a moderate antibacterial activity was recorded with both against Agrobacterium tumefaciens strains and Pseudomonas syringae pv. syringae.