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.